This commit performs two main changes:
* Alters the shaders to use only strictly conformant GLSL 2.0.
* Alters the Windows UI to use ANGLE via GL ES 2.0 and EGL 1.4.
This commit also drops official support for Windows XP, since ANGLE
requires a non-XP toolset to build. It is still possible to build
SolveSpace for Windows XP using:
cmake -T v120_xp -DOPENGL=1
This commit does three things:
* Recognizes that BeginFrame()/EndFrame() are badly named, since
BeginFrame() sets up framebuffer, and EndFrame() flushes a frame,
and they do not have to be called in pairs; and so renames them
to NewFrame()/FlushFrame().
* Reduces the amount of frame flushes in GraphicsWindow::Paint()
to two, which is the minimum since we use two different cameras
for geometry and UI;
* Changes the FPS measurement code to only take into account
the time spent rendering our main geometry, and not the UI
rendering or window system interaction time.
Before this commit, tooltips in the text window are drawn under
the red "X" indicating a disabled button. After this commit, they
are moved on top of that.
This commit also alters the OpenGL renderers' SetCamera() method
to clear the depth buffer, as that would interfere with drawing
the UI; the toolbar would get occluded by geometry.
There are two main reasons to desire an OpenGL 2 renderer:
1. Compatibility. The compatibility profile, ironically, does not
offer a lot of compatibility, and our OpenGL 1 renderer will not
run on Android, iOS, or WebGL.
2. Performance. The immediate mode does not scale, and in fact
becomes very slow with only a moderate amount of lines on screen,
and only a somewhat large amount of triangles.
This commit implements a basic OpenGL 2 renderer that uses only
features from the (OpenGL 3.2) core profile. It is not yet faster
than the OpenGL 1 renderer, primarily because it uses a lot of small
draw calls.
This commit uses OpenGL 2 on Linux and Mac OS X directly (i.e. links
to the GL symbols from version 2+); on Windows this is impossible
with the default drivers, so for now OpenGL 1 is still used there.
