OpenGL-Backend.md

+The OpenGL-specific parts of the hardware renderer are partially separated into the OpenGL backend. Ideally this would allow easier adaptation to other 3D rendering APIs by just implementing a new backend for it.
+
+OpenGL backend functions:
+
+`void Init (void)`
+
+`void SetTexture (GLMipmap_t *TexInfo)`
+
+`TexInfo` becomes the current texture, used in future draw calls. If NULL, then a white texture is used. The texture will be uploaded to the GPU if it has not been yet.
+
+`void UpdateTexture (GLMipmap_t *TexInfo)`
+
+Updated data from `TexInfo` is uploaded to the GPU. (`TexInfo` is left as the current texture?)
+
+`void DeleteTexture (GLMipmap_t *TexInfo)`
+
+`TexInfo` is deleted from the GPU.
+
+`void ClearMipMapCache (void)`
+
+All textures are deleted from the GPU.
+
+`INT32 GetTextureUsed (void)`
+
+Returns the number of bytes used by the textures uploaded to the GPU.
+
+
+`void SetPalette (RGBA_t *ppal)`
+`void SetSpecialState (hwdspecialstate_t IdState, INT32 Value)`
+`void GClipRect (INT32 minx, INT32 miny, INT32 maxx, INT32 maxy, float nearclip)`
+`void SetTransform (FTransform *ptransform)`
+
+`void SetBlend (FBITFIELD PolyFlags)`
+
+`void ClearBuffer (FBOOLEAN ColorMask, FBOOLEAN DepthMask, FRGBAFloat *ClearColor)`
+`void Draw2DLine (F2DCoord *v1, F2DCoord *v2, RGBA_t Color)`
+`void DrawPolygon (FSurfaceInfo *pSurf, FOutVector *pOutVerts, FUINT iNumPts, FBITFIELD PolyFlags)`
+`void DrawIndexedTriangles (FSurfaceInfo *pSurf, FOutVector *pOutVerts, FUINT iNumPts, FBITFIELD PolyFlags, UINT32 *IndexArray)`
+
+`void RenderSkyDome (gl_sky_t *sky)`
+
+`void FlushScreenTextures (void)`
+`void StartScreenWipe (void)`
+`void EndScreenWipe (void)`
+`void DoScreenWipe (void)`
+`void DrawIntermissionBG (void)`
+`void MakeScreenTexture (void)`
+`void MakeScreenFinalTexture (void)`
+`void DrawScreenFinalTexture (int width, int height)`
+`void PostImgRedraw (float points[SCREENVERTS][SCREENVERTS][2])`
+
+`boolean CompileShaders (void)`
+`void CleanShaders (void)`
+`void SetShader (int type)`
+`void UnSetShader (void)`
+`void SetShaderInfo (hwdshaderinfo_t info, INT32 value)`
+`void LoadCustomShader (int number, char *code, size_t size, boolean isfragment)`
+
+`void DrawModel (model_t *model, INT32 frameIndex, INT32 duration, INT32 tics, INT32 nextFrameIndex, FTransform *pos, float scale, UINT8 flipped, UINT8 hflipped, FSurfaceInfo *Surface)`
+`void CreateModelVBOs (model_t *model)`
+
+`void ReadRect (INT32 x, INT32 y, INT32 width, INT32 height, INT32 dst_stride, UINT16 *dst_data)`
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