All, I have been doing some validation of the hardware driver that we have developed based on OpenGL ES and came up with some peculiar results when comparing it to software blending. When blitting ARGB surfaces, the software blending seems to be different for several of the src/dest blend function combinations when compared to OpenGL. Is there anyone here that worked on the software blender? I am trying to confirm that the results I see are expected.
In an attempt to establish the expected behavior, I hand blended the colors to verify the results and concluded that the hand calculated/blended colors most closely matched the OpenGL blender. Not all combinations of blending functions produced different results. These are some of the combinations that didn't produce the expected results: Src: DstAlpha Dst: SrcColor Src: DstAlpha Dst: 1-SrcColor Src: DstAlpha Dst: SrcAlpha Src: DstAlpha Dst: 1-SrcAlpha Src: 1-DstAlpha Dst: SrcColor Src: 1-DstAlpha Dst: 1-SrcColor Src: 1-DstAlpha Dst: SrcAlpha Src: 1-DstAlpha Dst: 1-SrcAlpha Src: DstColor Dst: SrcColor Src: DstColor Dst: 1-SrcColor Src: DstColor Dst: SrcAlpha Src: DstColor Dst: 1-SrcAlpha Src: 1- DstColor Dst: SrcColor Src: 1- DstColor Dst: 1-SrcColor Src: 1- DstColor Dst: SrcAlpha Src: 1- DstColor Dst: 1-SrcAlpha Src: SrcAlphaSat Dst:SrcColor Src: SrcAlphaSat Dst:1-SrcColor This doesn't include all possible combinations, only those valid in OpenGL ES. For an example, the following demonstrates the results that I see. The Blend equation is Color(final) = Color(src)*BlendFunction(src) + Color(dst)*BlendFunction(dst). BlendFunction(src) = DstAlpha BlendFunction(dst) = SrcColor R(final) = R(src)*A(dst)/255 + R(dst)*R(src)/255 G(final) = G(src)*A(dst)/255 + G(dst)*G(src)/255 B(final) = B(src)*A(dst)/255 + B(dst)*B(src)/255 A(final) = A(src)*A(dst)/255 + A(dst)*A(src)/255 Src Color: 0x6e728cff ARGB=110 114 140 255 Dst Color: 0x7c8cdb72 ARGB=124 140 219 114 R(final) = 114*124/255 + 140*114/255 = 55 + 63 = 118 G(final) = 140*124/255 + 219*140/255 = 68 + 120 = 188 B(final) = 255*124/255 + 114*255/255 = 124 + 114 = 238 A(final) = 110*124/255 + 124*110/255 = 53 + 53 = 106 To compare (ARGB): 079 085 127 179 Software 107 118 188 234 Hardware 106 118 188 238 Hand Calculation As can be seen in the calculations above, the software blender produces substantially different values compared to the expected result. The hardware and hand calculations are close. Can anyone help me to understand what is going on? This is for DirectFB 1.0.1. If someone wants to run this on DirectFB 1.4, that would be appreciated. Bryce Poole Intel Corporation
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