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gsdx-tc: add a big comment to explain the scaling of src in TC

This commit is contained in:
Gregory Hainaut 2015-06-27 16:39:44 +02:00
parent d29e375f72
commit 6ca7a802bf
1 changed files with 19 additions and 5 deletions
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22
plugins/GSdx/GSTextureCache.cpp
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@ -911,10 +911,24 @@ GSTextureCache::Source* GSTextureCache::CreateSource(const GIFRegTEX0& TEX0, con
GSVector4 dRect(0, 0, w, h);
// Try to extract a texture bigger than the RT. Current solution is to rescale the size
// of the texture to fit in the RT. In my opinion, it would be better to increase the size of
// the RT
// TODO investigate this code is correct (maybe linked to custom resolution?)
// Lengthy explanation of the rescaling code.
// Here an example in 2x:
// RT is 1280x1024 but only contains 512x448 valid data (so 256x224 pixels without upscaling)
//
// PS2 want to read it back as a 1024x1024 pixels (they don't care about the extra pixels)
// So in theory we need to shrink a 2048x2048 RT into a 1024x1024 texture. Obviously the RT is
// too small.
//
// So we will only limit the resize to the available data in RT.
// Therefore we will resize the RT from 1280x1024 to 1280x1024/2048x2048 % of the new texture
// size (which is 1280x1024) (i.e. 800x512)
// From the rendering point of view. UV coordinate will be normalized on the real GS texture size
// This way it can be used on an upscaled texture without extra scaling factor (only requirement is
// to have same proportion)
//
// FIXME: The scaling will create a bad offset. For example if texture coordinate start at 0.5 (pixel 0)
// At 2x it will become 0.5/128 * 256 = 1 (pixel 1)
if(w > dstsize.x)
{
scale.x = (float)dstsize.x / tw;