vo_opengl_old: reject 9-15 bit formats if textures have less than 16 bit

For 9-15 bit material, cutting off the lower bits leads to significant
quality reduction, because these formats leave the most significant bits
unused (e.g. 10 bit padded to 16 bit, transferred as 8 bit -> only
2 bits left). 16 bit formats still can be played like this, as cutting
the lower bits merely reduces quality in this case.

This problem was encountered with the following GPU/driver combination:

OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) 915GM x86/MMX/SSE2
OpenGL version string: 1.4 Mesa 9.0.1

It appears 16 bit support is rather common on GPUs, so testing the
actual texture depth wasn't needed until now. (There are some other Mesa
GPU/driver combinations which support 16 bit only when using RG textures
instead of LUMINANCE_ALPHA. This is due to OpenGL driver bugs.)

1 files changed, 2 insertions, 0 deletions

diff --git a/video/out/gl_common.h b/video/out/gl_common.h
index de893966df..4afc192343 100644
--- a/video/out/gl_common.h
+++ b/video/out/gl_common.h
@@ -318,6 +318,8 @@ struct GL {
     void (GLAPIENTRY *EnableClientState)(GLenum);
     void (GLAPIENTRY *DisableClientState)(GLenum);
     GLenum (GLAPIENTRY *GetError)(void);
+    void (GLAPIENTRY *GetTexLevelParameteriv)(GLenum, GLint, GLenum, GLint *);
+
 
     void (GLAPIENTRY *GenBuffers)(GLsizei, GLuint *);
     void (GLAPIENTRY *DeleteBuffers)(GLsizei, const GLuint *);