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From Jason Daly, "The DDS reader test for DXT1 images with 1-bit alpha wasn't thorough enough. It performed the first check (color_0 <= color_1), but it didn't actually scan the texel block to see if the transparent color (0x03) was there. As a result, DXT1 files without any alpha were getting switched to RGBA format (instead of being left just RGB).

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The attached code fixes this problem."
This commit is contained in:
Robert Osfield 2009-11-27 15:48:57 +00:00
parent b4562b0393
commit 9b3e02f4e9
1 changed files with 28 additions and 6 deletions
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34
src/osgPlugins/dds/ReaderWriterDDS.cpp
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@ -660,16 +660,38 @@ osg::Image* ReadDDSFile(std::istream& _istream)
{
const DXT1TexelsBlock *texelsBlock = reinterpret_cast<const DXT1TexelsBlock*>(imageData);
// Only do the check on the first mipmap level
for ( int i = size / sizeof( DXT1TexelsBlock ); i>0; --i, ++texelsBlock )
// Only do the check on the first mipmap level, and stop when we
// see the first alpha texel
int i = size / sizeof(DXT1TexelsBlock);
bool foundAlpha = false;
while ((!foundAlpha) && (i>0))
{
// See if this block might contain transparent texels
if (texelsBlock->color_0<=texelsBlock->color_1)
{
// Texture is using the 1-bit alpha encoding, so we need to update the assumed pixel format
internalFormat = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
pixelFormat = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
break;
// Scan the texels block for the '11' bit pattern that
// indicates a transparent texel
int j = 0;
while ((!foundAlpha) && (j < 32))
{
// Check for the '11' bit pattern on this texel
if ( ((texelsBlock->texels4x4 >> j) & 0x03) == 0x03)
{
// Texture is using the 1-bit alpha encoding, so we
// need to update the assumed pixel format
internalFormat = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
pixelFormat = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
foundAlpha = true;
}
// Next texel
j += 2;
}
}
// Next block
--i;
++texelsBlock;
}
}