+ if (texImage->_BaseFormat == GL_LUMINANCE ||
+ texImage->_BaseFormat == GL_INTENSITY ||
+ texImage->_BaseFormat == GL_LUMINANCE_ALPHA) {
+ /* If a luminance (or intensity) texture is read back as RGB(A), the
+ * returned value should be (L,0,0,1), not (L,L,L,1). Set rebaseFormat
+ * here to get G=B=0.
+ */
+ rebaseFormat = texImage->_BaseFormat;
+ }
+ else if ((texImage->_BaseFormat == GL_RGBA ||
+ texImage->_BaseFormat == GL_RGB ||
+ texImage->_BaseFormat == GL_RG) &&
+ (destBaseFormat == GL_LUMINANCE ||
+ destBaseFormat == GL_LUMINANCE_ALPHA ||
+ destBaseFormat == GL_LUMINANCE_INTEGER_EXT ||
+ destBaseFormat == GL_LUMINANCE_ALPHA_INTEGER_EXT)) {
+ /* If we're reading back an RGB(A) texture as luminance then we need
+ * to return L=tex(R). Note, that's different from glReadPixels which
+ * returns L=R+G+B.
+ */
+ rebaseFormat = GL_LUMINANCE_ALPHA; /* this covers GL_LUMINANCE too */
+ }
+ else if (texImage->_BaseFormat != texBaseFormat) {
+ /* The internal format and the real format differ, so we can't rely
+ * on the unpack functions setting the correct constant values.
+ * (e.g. reading back GL_RGB8 which is actually RGBA won't set alpha=1)
+ */
+ switch (texImage->_BaseFormat) {
+ case GL_RED:
+ if ((texBaseFormat == GL_RGBA ||
+ texBaseFormat == GL_RGB ||
+ texBaseFormat == GL_RG) &&
+ (destBaseFormat == GL_RGBA ||
+ destBaseFormat == GL_RGB ||
+ destBaseFormat == GL_RG ||
+ destBaseFormat == GL_GREEN)) {
+ rebaseFormat = texImage->_BaseFormat;
+ break;
+ }
+ /* fall through */
+ case GL_RG:
+ if ((texBaseFormat == GL_RGBA ||
+ texBaseFormat == GL_RGB) &&
+ (destBaseFormat == GL_RGBA ||
+ destBaseFormat == GL_RGB ||
+ destBaseFormat == GL_BLUE)) {
+ rebaseFormat = texImage->_BaseFormat;
+ break;
+ }
+ /* fall through */
+ case GL_RGB:
+ if (texBaseFormat == GL_RGBA &&
+ (destBaseFormat == GL_RGBA ||
+ destBaseFormat == GL_ALPHA ||
+ destBaseFormat == GL_LUMINANCE_ALPHA)) {
+ rebaseFormat = texImage->_BaseFormat;
+ }
+ break;
+
+ case GL_ALPHA:
+ if (destBaseFormat != GL_ALPHA) {
+ rebaseFormat = texImage->_BaseFormat;
+ }
+ break;
+ }
+ }
+