Abstract:
A mobile terminal includes a display unit configured to display a screen generated by combining plural screen layers, four controllers connected to the display unit; wherein a first controller determines whether a transmission specification of a subject screen layer to be updated is enabled upon updating of the screen, a second controller determines whether a size of the subject screen layer to be updated is equal to or larger than a size of a screen displayed by the display unit when the first controller determines “YES”, a third controller determines whether the screen layer to be combined on a back surface of the subject screen layer to be updated exists when the second controller determines “YES”; and a fourth controller controls to disable the transmission specification of the subject screen layer to be updated when the third controller determines “NO”.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a mobile terminal capable of cancelling composition of the background layer based on the determination that the composition is unnecessary under the display control. 
         [0003]    2. Description of the Related Art 
         [0004]    Recently, the size of information data supplied to the user at a time has been increasing because of increased size of screen data accompanied with high definition of the display unit (display and the like) of such mobile terminal as the mobile phone. The time taken for the single updating of the screen has been prolonged and the power consumption has been increased owing to the increased screen data size on the display, resulting in deteriorated response to the user&#39;s operation and shortened battery life of the mobile terminal. 
         [0005]    Japanese Unexamined Patent Application Publication No. 2008-90645 discloses the information processor structured to save the device development cost and a device cost, and further to realize the power saving while improving visual perceptivity of the user. The information processor includes a display unit of a predetermined size, and at least two applications installed therein for outputting display data of a preset size to be displayed on the display unit. The processor further includes a display image data generation unit for generating image data for the display each having the identical size using the respective display data output from the applications, and an image composition output unit for composing the generated image data for the display by superposition so as to be output and displayed on the display unit. 
         [0006]    The image on the display of the mobile terminal is generated through composition of plural images (screen layers) The resultant performance is proportional to the number of the screen layers. In the generally employed mobile terminal, it is normally determined whether or not the transmission specification of the screen layer is enabled upon composition of the screen layers. However, it is generally designed to combine the background layer irrespective of the need of the background layer. Accordingly, it is preferable to design the mobile terminal to cancel composition of the background layer which is determined as being unnecessary while preventing the application program at the upper layer from correcting the error. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, it is an object of the present invention to provide a mobile terminal with improved screen updating performance without causing the application program at the upper layer to correct the error by cancelling the combination of the background layer which is determined as being unnecessary under the display control as well as with improved response to the user&#39;s operation by reducing the load. 
         [0008]    The present invention provides a mobile terminal which includes a display unit configured to display a screen generated by combining a plurality of screen layers, a controller connected to the display unit and including a first controller, a second controller, a third controller, and a fourth controller; wherein the first controller determines whether or not a transmission specification of a subject screen layer to be updated is enabled upon updating of the screen displayed by the display unit, the second controller determines whether or not a size of the subject screen layer to be updated is equal to or larger than a size of a screen displayed by the display unit when the first controller determines that the transmission specification is enabled, the third controller determines whether or not the screen layer to be combined on a back surface of the subject screen layer to be updated exists when the second controller determines that the size of the subject screen layer to be updated is equal to or larger than the size of the screen to be displayed by the display unit; and the fourth controller controls to disable the transmission specification of the subject screen layer to be updated when the third controller determines that the screen layer to be combined on the back surface does not exist. 
         [0009]    When the background layer composition is determined to be unnecessary under the display control, the mobile terminal according to the present invention is structured to improve the screen updating performance without causing the application program at the upper layer to correct the error by cancelling the composition, and to improve the response to the user&#39;s operation by reducing the load. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1A  is a front view of an mobile terminal (mobile phone) in an open state according to the present invention; 
           [0011]      FIG. 1B  is a side view of the mobile terminal (mobile phone) in an open state according to the present invention; 
           [0012]      FIG. 2A  is a front view of the mobile terminal (mobile phone) in a closed state according to the present invention; 
           [0013]      FIG. 2B  is a side view of the mobile terminal (mobile phone) in a closed state according to the present invention; 
           [0014]      FIG. 3  is a functional block diagram of the mobile terminal (mobile phone) according to the present invention; 
           [0015]      FIG. 4  is a view schematically showing the display control routine in the mobile terminal (mobile phone) according to the present invention; 
           [0016]      FIG. 5A  is a view showing an UI screen layer; 
           [0017]      FIG. 5B  is a view showing a multi-media screen layer; 
           [0018]      FIG. 5C  shows a result of combining the UI screen layer with the multi-media screen layer; 
           [0019]      FIG. 6  is a view schematically showing the display control routine in the mobile terminal (mobile phone) according to the present invention when the UI screen layer is in the transmissive mode, and the multi-media screen layer is in the non-transmissive mode; 
           [0020]      FIG. 7  is a flowchart showing the routine for combining the background layer under the display control of the mobile terminal (mobile phone) according to the present invention; 
           [0021]      FIG. 8  is a view schematically showing the display control routine in the mobile terminal (mobile phone) according to the present invention when the UI screen layer is in the transmissive mode, and the multi-media screen layer does not exist; 
           [0022]      FIG. 9  is a view schematically showing the display control routine in the mobile terminal (mobile phone) according to the present invention when the UI screen layer is in the non-transmissive mode, and the multi-media screen layer does not exist; 
           [0023]      FIG. 10  is a flowchart showing the process for cancelling the combination of the background layer under the display control routine executed in the mobile terminal (mobile phone) according to the present invention; 
           [0024]      FIG. 11  is a flowchart showing the display control routine upon updating of the screen layer in the mobile terminal (mobile phone) according to the present invention; 
           [0025]      FIG. 12  is a chart showing the data structure of the layer control information; 
           [0026]      FIG. 13  is a flowchart showing the display control routine when the screen layer is started in the mobile terminal (mobile phone) according to the present invention; and 
           [0027]      FIG. 14  is a flowchart showing the display control routine when finishing the screen layer in the mobile terminal (mobile phone) according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    An mobile terminal as an embodiment according to the present invention will be described referring to the drawings. A mobile phone  1  of clamshell type formed by connecting plural casings so as to be opened and closed will be described as an example of the terminal device according to the present invention.  FIG. 1A  is a front view of the mobile phone  1  in an open state, and  FIG. 1B  is a side view of the mobile phone  1  in the open state according to the present invention.  FIG. 2A  is a front view of the mobile phone  1  in a closed state, and  FIG. 2B  is a side view of the mobile phone  1  in the closed state. 
         [0029]    Referring to  FIGS. 1 and 2 , the mobile phone  1  is formed of a rectangular plate-like upper casing  10  and a lower casing  11  having substantially a same configuration as that of the upper casing  10 . Each of the upper casing  10  and the lower casing  11  has the surface covered with each other in the closed state. The upper and the lower casings  10  and  11  are hinged with a hinge portion  12  therebetween. The upper casing  10  is structured to be rotatable around the hinge portion  12  with respect to the lower casing  11  at a predetermined angle in an X direction shown in  FIGS. 1 and 2 . The state of the mobile phone  1  is changed from the open state to the closed state or vice versa by rotating the upper casing  10  with respect to the lower casing  11 . 
         [0030]    A display  13  for displaying the display information which includes characters and images is formed on the inner surface of the upper casing  10  (opposite the lower casing  11 ). The display  13  may be a liquid crystal display as a liquid crystal panel, or an organic EL display as the organic EL panel. The liquid crystal panel changes the direction (orientation) of the liquid crystal molecules by applying the voltage to the liquid crystal. The resultant orientation change serves to shutter the light so as to block or transmit the light from the light source such as the backlight for displaying the predetermined data. The organic EL panel is structured to display the data using light emission caused by exciton resulting from recombination of electron injected into the organic compound with the electron hole. A speaker  14  for outputting the sound is disposed on the inner surface of the upper casing  10 . 
         [0031]    Operation keys  15  including a power key for turning power ON/OFF, a call key for calling, a ten-key for inputting numerals and characters, a short cut key for activating the mail function and Web browser and the like are disposed on the inner surface (opposite the upper casing  10 ) of the lower casing  11 . A microphone  16  for collecting the sound is disposed on the inner surface of the lower casing  11 . 
         [0032]    Functions of the mobile phone  1  will be described referring to the block diagram shown in  FIG. 3 . The mobile phone  1  is formed by connecting a main control unit  20 , a power circuit  21 , an operation input control unit  22 , a display control unit  23 , a sound control unit  24 , a communication control unit  25 , a data storage unit  26 , and a TV receiving unit  27  via bus lines so as to be mutually communicated with one another. 
         [0033]    The main control unit  20  includes a CPU for performing various types of calculations to centrally control the mobile terminal  1  as well as perform display control to be described later and various calculation and control operations. The power circuit  21  turns the power ON/OFF based on the input performed by the user via the operation keys  15 . When the power is turned ON, power is supplied from the power supply source (battery) to the respective units so as to activate the mobile terminal  1 . 
         [0034]    The operation input control unit  22  includes an input interface to the operation keys  15 . When depression of any of the operation keys  15  is detected, the signal indicating the depressed key is generated, and transmitted to the main control unit  20 . The display control unit  23  includes a display interface to the display  13  for displaying the character and image on the display  13  under the control of the main control unit  20 . 
         [0035]    The sound control unit  24  generates an analog sound signal from the sound collected by the microphone  16  under the control of the main control unit  20  so as to be converted into a digital sound signal. The sound control unit  24  converts the thus obtained digital sound signal into the analog sound signal under the control of the main control unit  20  so as to be output as the sound from the speaker  14 . 
         [0036]    The communication control unit  25  subjects the reception signal received from the base station via an antenna  25   a  to spread spectrum inverse processing under the control of the main control unit  20  to decompress the data. The data are transmitted to the sound control unit  24  to be output from the speaker  14  in response to the command of the main control unit  20 , or transmitted to the display control unit  23  to be displayed on the display  13 . Alternatively, they are stored in the data storage unit  26 . Upon acquisition of the sound data collected by the microphone  17 , the data input via the operation key  15 , and the data stored in the data storage unit  26 , the communication control unit  25  subjects those data to spread spectrum processing under the control of the main control unit  20  so as to be transmitted to the base station via the antenna  25   a.    
         [0037]    The data storage unit  26  includes a ROM for storing processing program and data required for the processing, a hard disk, a non-volatile memory, a database, a RAM for temporarily storing data to be used upon the processing performed by the main control unit  20  and the like. The processing program for the display control processing performed by the main control unit  20  is designed to be stored in the ROM, for example. 
         [0038]    The TV receiving unit  27  includes a TV antenna  27   a  for receiving TV broadcasting wave such as the digital terrestrial one-segment broadcasting wave, the digital terrestrial broadcasting, and terrestrial 3-segment radio broadcasting wave from the broadcast station via the TV antenna  27   a.  The TV receiving unit  27  separates the received data with respect to those received TV broadcasting waves into the sound signal and the image signal to perform the TV visual processing by displaying the image signal on the display  13  by the display control unit  23 , and outputting the sound signal by the sound control unit  24  via the speaker  14 . 
         [0039]    Referring to  FIG. 4 , upon activation of the application program by the main control unit  20  in the mobile phone  1 , plural screen layers are produced under the control of the application program. Those screen layers include an UI (User Interface) screen layer  40  for displaying the information for the user to operate the mobile phone  1  and a multi-media screen layer  41  for displaying the video image. Those plural screen layers are combined by the display control unit  23  so as to be displayed on the display  13 . The UI screen layer  40  has the same size as that of the display screen  44  on the display  13 . 
         [0040]    The UI screen layer  40  includes a region for displaying such title as “Apr. 4, 2008 in Yokohama” on the display  13  as shown in  FIG. 5A , a region  40   a  for displaying the video image (region specified as being in the transmissive mode), and a region which includes a region  40   a  (transmission specified) to allow the multi-media screen layer  41  to display the video image as shown in  FIG. 5B . Referring to  FIG. 5C , composite display data  43  are formed by superimposing the UI screen layer  40  with the multi-media screen layer  41  which is put in the region  40   a  specified as being in the transmissive mode as a part of the UI screen layer  40 . 
         [0041]    The display control unit.  23  includes a driver  30  for allowing the display  13  to display the screen based on the screen layer generated by the main control unit  20 , and an FB  31  for temporarily storing the data displayed on the display  13 . When the driver  30  which includes a background layer  42  obtains plural screen layers from the main control unit  20 , those screen layers are combined with the background layer  42  to generate the composite display data  43  so as to be output to the FV  31 . The composite display data  43  are combined with the background layer  42  only at the time of need. 
         [0042]    The FB  31  includes a VRAM  32  which temporarily stores the composite display data  43  formed by the driver  30  so as to be displayed on the display  13 . 
         [0043]    In the mobile phone  1 , plural screen layers formed by the currently executed application programs are combined by the driver  30  under the control of the middleware. The composite result is transferred to the display  13  by the FB  31  so as to be displayed thereon. The content to be displayed on the display  13  is temporarily stored in the VRAM in the FB  31  for controlling the display  13 , and referred at an interval indicated by a predetermined refresh rate to be displayed on the display  13 . 
         [0044]    Generally in the case where the plural screen layers are combined, when one of those screen layers is required to be updated or specified to be in the transmissive mode, all the screen layers which constitute the screen are referred and combined again so as to be displayed on the display  13 . The screen layers are prepared by the number required to constitute the screen by executing the respective application programs. Actually, however, the background layer  42  held by the driver  30  is also combined in addition to those screen layers used by the application programs. 
         [0045]    When any one of the screen layers is specified to be in the transmissive mode, the screen layer on the back surface is combined. When the layer on the back surface is further specified to be in the transmissive mode, the screen layer on the back surface is combined. The combining operation is repeatedly performed to finally combine the background layer  42  to form the composite display data  43 . The need of setting the transmissive mode is specified for each of the screen layers, and is determined upon generation of the screen layer by the application program. 
         [0046]    There are plural ways to realize the transmission from the processes (1) to (3) as follows. 
         [0047]    (1) The specific color is defined as a color to be transmissive. 
         [0048]    (2) The transmittance is set for each layer. 
         [0049]    (3) The transmittance is set for each pixel. 
         [0050]    Each setting of the aforementioned processes is kept unchanged irrespective of the condition of the data to be combined. That is, the specific color (case ( 1 )), the fixed transmittance (case ( 2 )), and the transmittance in accordance with the content to be displayed, that is, screen design (case ( 3 )) may be set. Each setting of the processes (1) to (3) may be kept unchanged irrespective of the condition of the data to be combined. However, the color to be transmissive (case ( 1 )), and the transmittance (case ( 2 ) or ( 3 )) may be changed depending on the condition without being limited to the aforementioned setting. 
         [0051]    The screen layer entirely filled in a specific color is used as the background layer  42 . In such a case, the transmissive color in the case ( 1 ) is the same as or close to the color for filling the background layer  42 . When the user of the screen layer (application program) requires the transmission in the aforementioned state, that is, when the transmission specification is enabled, the transmission specification of the subject screen layer is disabled by the middleware if the other screen layer is not combined with the back surface of the subject screen layer. The region filled in the transmissive color is supposed to have the color of the background layer  42  displayed. When the transmission specification is disabled, the transmissive color is displayed without being transmitted. However, as the transmissive color is the same as that of the background layer  42 , those colors are apparently the same for the user. When the transmission specification is disabled, the combining operation by the driver  30  and subsequent process may be cancelled to allow the mobile phone  1  to execute the display control for a shorter period. 
         [0052]    The request for the screen update from the application program is indirectly sent to the driver  30  via the middleware. The request to the driver  30  may be changed based on the determination with respect to the screen layer structure by the middleware to optimize such request to the driver  30  while keeping the application program less conscious about the processing. 
         [0053]    The middleware is allowed to disable the transmission specification only when the following conditions (4) to (6) are satisfied. 
         [0054]    (4) The transmission specification of the subject screen layer to be updated is set as defined in the case ( 1 ). 
         [0055]    (5) The image allocated to the subject screen layer to be updated covers the entire screen  44  on the display  13 . 
         [0056]    (6) The screen layer in use does not exist on the back surface of the subject screen layer to be updated. 
         [0057]    The timing for which the middleware makes the determination may be defined as one of the following timings (7) and (8). 
         [0058]    (7) Timing when the attribute information (transmission specification) with respect to the screen layer changes. 
         [0059]    (8) Timing when the request for starting/finishing the use of the screen layer is generated. 
         [0060]    Referring to  FIG. 6 , in the case where the transmission specification of the UI screen layer  40  is “enabled”, the transmission specification of the multi-media screen layer  41  is “disabled”, and the size of the media screen layer  41  is smaller than that of the display, the middleware enables the transmission specification in accordance with the setting established by the application program to allow the driver  30  to combine the UI screen layer  40 , the multi-media screen layer  41 , and the background layer  42  to generate the composite display data  43 . As shown in  FIG. 7 , the driver  30  performs the following operations, that is, copies the content of the background layer  42  on the screen of the composition display data  43  (operation (A)), and copies the content of the UI screen layer  40  to the composite display data  43  while determining with respect to the transmission (operation (B)). 
         [0061]    Referring to  FIG. 8 , in the case where the transmission specification of the UI screen layer  40  is “enabled”, and any other screen layer does not exist on the back surface, the middleware disables the transmission specification (the setting of the “transmissive mode” may be changed to the “non-transmissive mode”) to cancel the processing performed by the driver  30  for combining the background layer  42 . In the aforementioned case, the driver  30  copies the content of the UI screen layer  40  on the screen of the composite display data  43  (operation (C)). Even if the “transmissive mode” is set, the transmissive portion has the same color as that of the background layer  42  or the color similar thereto. So the same result may be obtained even when the screen of the background layer  42  is combined. The aforementioned combining operation is cancelled for the purpose of reducing the calculation work. 
         [0062]    Referring to  FIG. 9 , in the case where the transmission specification of the UI screen layer  40  is “disabled”, the middleware cancels the combining operation of the background layer  42  performed by the driver  30  while keeping the transmission specification disabled. In the aforementioned case, the driver  30  performs the operation (C), that is, copies the content of the UI screen layer  40  on the screen of the composite display data  43 . 
         [0063]    The mobile phone  1  is structured to allow the middleware to change the transmission specification of the respective screen layers based on the states of the plural screen layers formed by the currently executed application program. As a result, the updating performance of the screen may be improved without modifying the application program to be executed. The procedure of the display control routine executed by the mobile phone  1  will be described referring to the flowchart shown in  FIG. 11 . The term “step S 101 ” will be referred to as “S 101 ” by omitting “step” hereinafter. 
         [0064]    The display control processing upon the change in the attribute information (transmission specification) with respect to the screen layer will be described. When the mobile phone  1  is operated, for example, when the user inputs through the operation keys  15 , receives data through the mail/browser, or ends the currently executed process to require the rewiring of the display screen  44  on the display  13 , the main control unit  20  generates the screen layer of the display screen  44  under the control of the application program, and sets the transmission specification of each screen layer based on the control executed by the middleware. 
         [0065]    The main control unit  20  obtains layer control information  50  of the subject layer (screen layer having the attribute information changed) (S 101 ). The layer control information  50  is controlled by the middleware for each array by the number of the layers, and contains the layer number, width, height, color depth (color number), layer attribute, buffer address, handle value, activated state, rotating index, transmission specification and the like. 
         [0066]    The layer number is the information which denotes the layer identifier as well as the order of the screen layer (for example, the screen layer on the rearmost surface is set to “0”, and “1” is incremented as the layer is increased forward). The layer attribute is the information which indicates whether the layer is the UI screen layer or the multi-media screen layer. If the layer attribute indicates the UI screen layer, the usage is fixed. So the middleware holds the image buffer to be sent to the driver. If the layer attribute indicates the multi-media screen layer, the screen size or the number of the frame screens becomes variable. So the middleware holds no buffer. 
         [0067]    The handle value is issued when the screen layer is in use, and serves as the information which indicates the user of the screen layer. The activated state is the information which indicates whether or not the screen layer is in use (whether or not it is actually used in the application program). When the screen layer is used (formed), it is used for controlling whether or not the issued handle value is actually displayed. The rotating index is the information indicating presence/absence of the rotating display. If the screen layer includes the transmissive region, the transmission specification is “enabled”, and if the screen layer includes no transmissive region, the transmission specification is “disabled”. 
         [0068]    The main control unit  20  determines whether or not the transmission of the subject layer is specified (S 102 ). When the transmission specification of the layer control information  50  obtained in step S 101  is “enabled”, it is determined that the transmission of the subject layer has been specified. When the transmission of the subject layer is not specified (No in  3102 ), the main control unit  20  disables the transmission specification (S 103 ). The driver  30  is allowed to cancel the combining operation of the background layer  42 . 
         [0069]    When the transmission of the subject layer is specified (Yes in S 102 ), the main control unit  20  determines whether or not the size of the subject layer is equal to or larger than that of the screen  44  on the display  13  (S 105 ). At this time, the main control unit  20  makes the determination based on the width and the height of the layer control information  50  acquired in step S 101 . 
         [0070]    When the size of the subject layer is not equal to or larger than that of the screen  44  (No in S 105 ), the subject layer has the size smaller than that of the screen  44  on the display  13 . Accordingly, the subject layer is required to be combined with the other screen layer or the background layer  42 . So the main control unit  20  enables the transmission specification (S 107 ). 
         [0071]    When the size of the subject layer is equal to or larger than that of the screen  44  (Yes in S 105 ), the main control unit  20  sets the subject layer as “A” (S 109 ). The main control unit  20  obtains the layer at the back side of the layer A set in step S 109  or S 117  so as to be set as “B” (S 111 ). 
         [0072]    The main control unit  20  determines whether or not the screen layer B set in step S 109  exists (S 113 ). At this time, the main control unit  20  determines whether or not the screen layer B exists based on the handle value of the layer control information  50  obtained in step S 101 . When the screen layer B does not exist (No in S 113 ), the main control unit  20  disables the transmission specification (S 103 ) to allow the driver  30  to cancel the combining operation of the background layer  42 . 
         [0073]    When the layer B exists (Yes in S 113 ), the main control unit  20  determines whether or not the layer B is in use (S 115 ). At this time, the main control unit  20  makes the determination whether or not the screen layer A is in use based on the activated state of the layer control information  50  obtained in step S 109 . 
         [0074]    When the layer B is in use (Yes in S 115 ), the other screen layer is combined with the back surface of the subject layer. Then the main control unit  20  enables the transmission specification (S 107 ) to allow the driver  30  to combine the background layer  42 . 
         [0075]    When the layer B is not in use (No in S 115 ), the main control unit  20  sets the layer B set in step S 111  as A (S 117 ). Then the process returns to step S 111  where the main control unit  20  determines whether or not the layer B exists. 
         [0076]    In the case where the screen layer to be combined with the screen  44  on the display  13  in the mobile phone  1 , the middleware determines with respect to the structure state of the screen layer. Even if the subject layer has the size smaller than that of the screen  44  on the display  13 , or the screen layer on the back surface is in use, the transmission specification is kept enabled. When the screen layer on the back surface does not exist, the transmission specification is disabled. 
         [0077]    The procedure for the display control upon start of the use of the screen layer in the mobile phone  1  will be described referring to the flowchart shown in  FIG. 13 . When the use of the screen layer is started, and the started screen layer is positioned on the rearmost surface, the determination with respect to the transmission specification of the front screen layer is made again under the control of the middleware to specify the transmissive mode again. 
         [0078]    The main control unit  20  updates the layer control information  50  stored in the middleware (S 201 ). At this time, the information with respect to the started screen layer is updated in the layer control information  50 . The main control unit  20  sets the subject layer (the use of the screen layer is started) as the layer A (S 203 ). 
         [0079]    The main control unit  20  determines whether or not the screen layer A set in step S 203  or S 213  corresponds to the one on the rearmost surface (S 205 ). The main control unit  20  makes the determination based on the layer number of the layer control information  50  updated in step S 201 . When the screen layer A does not correspond to the one on the rearmost surface (No in S 205 ), the main control unit  20  ends the routine. 
         [0080]    When the screen layer A corresponds to the one on the rearmost surface (Yes in S 205 ), the main control unit  20  sets the screen layer positioned one surface forward of the screen layer A set in step S 203  or S 213  as the screen layer “B” (S 207 ). 
         [0081]    The main control unit  20  determines whether or not the screen layer B set in step S 207  exists (S 209 ). The main control unit  20  makes the determination based on the handle value of the layer control information  50  set in step S 201 . When the screen layer B does not exist (No in S 209 ), the main control unit  20  ends the routine. 
         [0082]    When the screen layer B exists (Yes in S 209 ), the main control unit  20  determines whether or not the layer B set in step S 207  is in use (S 211 ). The main control unit  20  makes the determination based on the activated state of the layer control information  50  updated in step S 201 . 
         [0083]    When the screen layer B is not in use (No in S 211 ), the main control unit  20  sets the screen layer B as the screen layer “A” (S 213 ). The process returns to step S 207  where the main control unit  20  executes the process from steps  3209  to S 219  having the screen layer positioned one surface forward of the screen layer A set in step S 213  set as “B”. 
         [0084]    When the screen layer B is in use (Yes in S 211 ), the main control unit  20  determines whether or not transmission of the screen layer B set in step S 207  is specified (S 215 ). The main control unit  20  determines that transmission of the subject layer is specified when the transmission specification of the layer control information  50  updated in step S 201  is “enabled”. 
         [0085]    When transmission of the screen layer B set in step S 207  is specified (Yes in S 215 ), the subject layer is required to be combined with the other screen layer or the background layer  42 . So the main control unit  20  enables the transmission specification (S 217 ). Meanwhile, when transmission of the screen layer B set in step S 207  is not specified (No in S 215 ), the subject layer does not have to be combined with the other screen layer or the background layer  42 . So the main control unit  20  disables the transmission specification (S 219 ). 
         [0086]    Upon start of the use of the screen layer to be combined with the screen  44  on the display  13  in the mobile phone  1 , if the subject layer corresponds to the one on the rearmost surface, and the transmission specification of the screen layer on the front surface is enabled, the transmission specification is kept enabled even if the transmission specification of the subject layer has been enabled. Meanwhile, if the subject layer is the one on the rearmost surface, and the transmission specification of the screen layer on the front surface is disabled, the transmission specification is disabled. 
         [0087]    The procedure for the display control process when the use of the screen layer is finished in the mobile phone  1  will be described referring to the flowchart shown in  FIG. 14 . When the use of the screen layer is finished, and the finished screen layer corresponds to the one on the rearmost surface, the transmission specification of the screen layer on the front surface is determined again under the control of the middleware to specify the transmission mode again. 
         [0088]    The main control unit  20  updates the layer control information  50  stored in the middleware (S 301 ). The information of the layer control information  50  with respect to the finished screen layer is updated. The main control unit  20  sets the subject layer (the screen layer having its use finished) as “A” (S 303 ). 
         [0089]    The main control unit  20  determines whether or not the screen layer A set in step S 303  or S 313  corresponds to the one on the rearmost surface (S 305 ). The main control unit  20  makes the determination based on the layer number of the layer control information  50  updated in step S 301 . When the screen layer A does not correspond to the one on the rearmost surface (No in S 305 ), the main control unit  20  ends the routine. 
         [0090]    When the screen layer A corresponds to the one on the rearmost surface (Yes in S 305 ), the main control unit  20  sets the screen layer positioned one surface forward of the screen layer A set in step S 303  or S 313  as “B” (S 307 ). 
         [0091]    The main control unit  20  determines whether or not the screen layer B set in step S 307  exists (S 309 ). The main control unit  20  makes the determination based on the handle value of the layer control information  50  updated in step S 301 . When the screen layer B does not exist (No in S 309 ), the main control unit  20  ends the routine. 
         [0092]    When the screen layer B exists (Yes in S 309 ), the main control unit  20  determines whether or not the layer B set in step S 307  is in use (S 311 ). The main control unit  20  makes the determination based on the activated state of the layer control information  50  updated in step S 301 . 
         [0093]    When the screen layer B is not in use (No in S 311 ), the main control unit  20  changes the screen layer B to the screen layer “A” (S 313 ). The process returns to step S 207  where the main control unit  20  executes the process from steps S 309  to S 321  while setting the screen layer positioned one surface forward of the screen layer of A set in step S 213  as “B”. 
         [0094]    When the screen layer B is in use (Yes in S 311 ), the main control unit  20  determines whether or not the transmission of the screen layer B set in step S 307  is specified (S 315 ). The main control unit  20  determines that the transmission of the subject layer is specified when the transmission specification of the layer control information  50  updated in step S 301  is “enabled”. 
         [0095]    When the transmission of the screen layer B set in step S 307  is specified (Yes in S 315 ), the main control unit  20  determines whether or not the size of the subject layer is equal to or larger than that of the screen  44  on the display  13  (S 317 ). The main control unit  20  makes the determination based on the width and height of the layer control information  50  in step S 301 . 
         [0096]    When the transmission of the layer B is specified, and the size of the subject layer is not equal to or larger than that of the screen  44  on the display  13  (No in S 317 ), the main control unit  20  enables the transmission specification (S 319 ). When the transmission specification on the screen layer B set in step S 307  does not exist (No in S 315 ), or the size of the subject layer is equal to or larger than that of the screen  44  on the display  13  (Yes in S 317 ), the main control unit  20  enables the transmission specification (S 321 ). 
         [0097]    When finishing the use of the screen layer to be combined with the screen  44  on the display  13  in the mobile phone  1 , the middleware determines with respect to the screen layer structure while having the transmission specification of the subject layer enabled. Irrespective of the aforementioned state, when the subject layer is the one on the rearmost surface, the transmission specification of the screen layer on the front surface is enabled, and the size of the subject layer is smaller than that of the screen  44 , the transmission specification is enabled. When the subject layer is the one on the rearmost surface and the transmission specification of the screen layer on the front surface is disabled, or when the subject layer is the one on the rearmost surface, the transmission specification of the screen layer on the front surface is enabled, and the size of the subject layer is equal to or larger than that of the screen  44 , the transmission specification is disabled. 
         [0098]    In the mobile terminal (mobile phone  1 ) according to the present invention, composition of the background layer may be cancelled when it is unnecessary under the display control. This may improve the updating performance of the screen requiring no need of correction of the upper application program, and further improve the response to the user&#39;s operation by reducing the load. 
         [0099]    The mobile phone  1  according to the present invention has been described. However, the mobile terminal of any type, for example, PHS, PDA, a PC, a music player, a digital camera, and a game machine may be employed so long as the image display processing is performed.