add Impl version for SalGraphics

Using an Impl pattern here allows us to switch the rendering in each
plugin without introducing any additional plugins.

The SalGraphics subclass will just forward the rendering call to the
Impl which can either be the normal native one or the OpenGL one.

Change-Id: Id234c60335305bfb42bf3d2b912f02d1f542bd06
use Impl for unix vcl plugins

Change-Id: I110df787e1d4b817ab6e682fd9bf50a24332fafd
we need to export the SalGraphicsImpl class

Change-Id: I569a1aacdb7a87b0e8045863a8569520bd0df09a
no need for these methods to be virtual

Change-Id: I23413704b27474f6a59121bb1cbf24ee7484acd2
add missing header guards

Change-Id: I73f7a25a180696b8581e673de8f39dd007fe5358
forgot to populate the Impl

Change-Id: Ic7b49a06f5e4576c29b74d86e4025e21a01dc53d
implement stub for OpenGL SalGraphicsImpl sub class

Change-Id: I8267bd26e1542230b9c112d741bba68d541b3994
it is false and not FALSE

Change-Id: I63c0cf97376d2aa4e27bed3e731b82af51b86804
use Impl for windows backend

Change-Id: Ie354aaf11644122754b69bc303c781297cacdc77
integrate WIP OpenGL rendering to unix backend

for now can be enabled with USE_OPENGL environment variable

Change-Id: I3d2c49c3a1cf0c06678b22addcab95c846bb7bf9
fix double delete after latest refactoring

Change-Id: Ie9cae6ee3769631f9095a5995d5165d5367aa2b0
fix missing pieces

That resulted in the wrong color used for some rendering.

Change-Id: I1f427fb65e287d17ca96ea6adbc46686f48f8c6f
use m prefix instead of _ for member variables

Change-Id: I9f73d653f3b5a4ec3eea91398977d4dfc2d478e7
reduce one use of SystemWinData

Change-Id: I777a8e324864ab9eab2a3df3e0645910dd1478a4
split method in part related to windows and other stuff

Change-Id: Ie3851bfd558ffeabd374afdc2a4d4833e3866a6e
add a OpenGLContext::init for unix backend

That one does not need the indirection through a Window instance to get
to the X resources that are necessary for a GLX context.

Change-Id: I3195a5f2b447172434881bd9b0b230c8992c1c87
add a OpenGLContext to unix backend

Change-Id: I71a3e3e12aad88714b37116bc2a619df75277588
merge vcllo and vclopengllo

Change-Id: I419ca67dc1f87dd9ac751aa5a094fecf58136edb
add OpenGLContext to OpenGL vcl rendering code

Change-Id: I05d1033c04d892638262d4a6a3e76897470e1467
that should be a SAL_WARN

Change-Id: I331b635c1e5518e4fd70a5b6bf5ced7cbc51782a