* Return list of (and count of) all specific texture compression
* formats that are supported.
*
+ * Some formats are \b not returned by this function. The
+ * \c GL_COMPRESSED_TEXTURE_FORMATS query only returns formats that are
+ * "suitable for general-purpose usage." All texture compression extensions
+ * have taken this to mean either linear RGB or linear RGBA.
+ *
+ * The GL_ARB_texture_compress_rgtc spec says:
+ *
+ * "19) Should the GL_NUM_COMPRESSED_TEXTURE_FORMATS and
+ * GL_COMPRESSED_TEXTURE_FORMATS queries return the RGTC formats?
+ *
+ * RESOLVED: No.
+ *
+ * The OpenGL 2.1 specification says "The only values returned
+ * by this query [GL_COMPRESSED_TEXTURE_FORMATS"] are those
+ * corresponding to formats suitable for general-purpose usage.
+ * The renderer will not enumerate formats with restrictions that
+ * need to be specifically understood prior to use."
+ *
+ * Compressed textures with just red or red-green components are
+ * not general-purpose so should not be returned by these queries
+ * because they have restrictions.
+ *
+ * Applications that seek to use the RGTC formats should do so
+ * by looking for this extension's name in the string returned by
+ * glGetString(GL_EXTENSIONS) rather than
+ * what GL_NUM_COMPRESSED_TEXTURE_FORMATS and
+ * GL_COMPRESSED_TEXTURE_FORMATS return."
+ *
+ * There is nearly identical wording in the GL_EXT_texture_compression_rgtc
+ * spec.
+ *
+ * The GL_EXT_texture_rRGB spec says:
+ *
+ * "22) Should the new COMPRESSED_SRGB_* formats be listed in an
+ * implementation's GL_COMPRESSED_TEXTURE_FORMATS list?
+ *
+ * RESOLVED: No. Section 3.8.1 says formats listed by
+ * GL_COMPRESSED_TEXTURE_FORMATS are "suitable for general-purpose
+ * usage." The non-linear distribution of red, green, and
+ * blue for these sRGB compressed formats makes them not really
+ * general-purpose."
+ *
+ * The GL_EXT_texture_compression_latc spec says:
+ *
+ * "16) Should the GL_NUM_COMPRESSED_TEXTURE_FORMATS and
+ * GL_COMPRESSED_TEXTURE_FORMATS queries return the LATC formats?
+ *
+ * RESOLVED: No.
+ *
+ * The OpenGL 2.1 specification says "The only values returned
+ * by this query [GL_COMPRESSED_TEXTURE_FORMATS"] are those
+ * corresponding to formats suitable for general-purpose usage.
+ * The renderer will not enumerate formats with restrictions that
+ * need to be specifically understood prior to use."
+ *
+ * Historically, OpenGL implementation have advertised the RGB and
+ * RGBA versions of the S3TC extensions compressed format tokens
+ * through this mechanism.
+ *
+ * The specification is not sufficiently clear about what "suitable
+ * for general-purpose usage" means. Historically that seems to mean
+ * unsigned RGB or unsigned RGBA. The DXT1 format supporting alpha
+ * (GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) is not exposed in the list (at
+ * least for NVIDIA drivers) because the alpha is always 1.0 expect
+ * when it is 0.0 when RGB is required to be black. NVIDIA's even
+ * limits itself to true linear RGB or RGBA formats, specifically
+ * not including EXT_texture_sRGB's sRGB S3TC compressed formats.
+ *
+ * Adding luminance and luminance-alpha texture formats (and
+ * certainly signed versions of luminance and luminance-alpha
+ * formats!) invites potential comptaibility problems with old
+ * applications using this mechanism since old applications are
+ * unlikely to expect non-RGB or non-RGBA formats to be advertised
+ * through this mechanism. However no specific misinteractions
+ * with old applications is known.
+ *
+ * Applications that seek to use the LATC formats should do so
+ * by looking for this extension's name in the string returned by
+ * glGetString(GL_EXTENSIONS) rather than
+ * what GL_NUM_COMPRESSED_TEXTURE_FORMATS and
+ * GL_COMPRESSED_TEXTURE_FORMATS return."
+ *
+ * There is no formal spec for GL_ATI_texture_compression_3dc. Since the
+ * formats added by this extension are luminance-alpha formats, it is
+ * reasonable to expect them to follow the same rules as
+ * GL_EXT_texture_compression_latc. At the very least, Catalyst 11.6 does not
+ * expose the 3dc formats through this mechanism.
+ *
* \param ctx the GL context
* \param formats the resulting format list (may be NULL).
- * \param all if true return all formats, even those with some kind
- * of restrictions/limitations (See GL_ARB_texture_compression
- * spec for more info).
*
* \return number of formats.
*/
GLuint
-_mesa_get_compressed_formats(struct gl_context *ctx, GLint *formats, GLboolean all)
+_mesa_get_compressed_formats(struct gl_context *ctx, GLint *formats)
{
GLuint n = 0;
if (ctx->Extensions.TDFX_texture_compression_FXT1) {
n += 2;
}
}
- /* don't return RGTC - ARB_texture_compression_rgtc query 19 */
+
if (ctx->Extensions.EXT_texture_compression_s3tc) {
if (formats) {
formats[n++] = GL_COMPRESSED_RGB_S3TC_DXT1_EXT;
- /* This format has some restrictions/limitations and so should
- * not be returned via the GL_COMPRESSED_TEXTURE_FORMATS query.
- * Specifically, all transparent pixels become black. NVIDIA
- * omits this format too.
- */
- if (all)
- formats[n++] = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
formats[n++] = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
formats[n++] = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
}
else {
n += 3;
- if (all)
- n += 1;
}
}
if (ctx->Extensions.S3_s3tc) {
n += 4;
}
}
-#if FEATURE_EXT_texture_sRGB
- if (ctx->Extensions.EXT_texture_sRGB) {
- if (formats) {
- formats[n++] = GL_COMPRESSED_SRGB_S3TC_DXT1_EXT;
- formats[n++] = GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT1_EXT;
- formats[n++] = GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT;
- formats[n++] = GL_COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT;
- }
- else {
- n += 4;
- }
- }
-#endif /* FEATURE_EXT_texture_sRGB */
return n;
#if FEATURE_ES1 || FEATURE_ES2
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