I'm looking into the details of ASTC and planning for developing in hardware. The spec version 1.0 says it has LDR & full profile. What is the difference between LDR & HDR modes? What is Full profile then ?
How does each modes process data. What is the input data format of LDR mode ? Is HDR accepts only 32bit ieee 784 floating point numbers ? How many partitions a block can have ? How about the decoding, the spec says it has to be bit exact decode. If lot of floating point operations are required, then is it possible to get bit exact decoding, because of approximation of fixed point implementation for floating point calculations ?
Hi Sean,
ASTC decoder always outputs the data as 4 components (ARGB). For example the image is GRAY still it outputs as ARGB. Is this a requirement for GPU hardware ?
Is it possible to have block level color settings, for example Block 0 is luma, Block 1 RGB, Block 2 Luminance + Alpha, Block 3 ARGB ?
What is the use of swizzle pattern in astc ?
is sRGB conversion mandatory as part of ASTC or can be handled at display side ?
-ben
Could you please respond
Ben,
Again, sorry for the slow response - I had a few days off to move house, and am currently on the road in the USA.
Yes, the ASTC decoder always decodes to RGBA as this is what is passed from the texture unit into the OpenGL ES Shading Language. A sampler will always return a vec4 of appropriate type, with appropriate conversions. A luminance-only texture access that returns value L will be actually be passed to the pipeline as {r,g,b,a}={L,L,L,1}. This is so that the shader code and the sampler type can be separately specified without having to recompile the shader, which could be costly.
Each block has its own color endpoint modes, so you are correct. Imagine, for example, encoding a picture of the Amundsen Scott South Pole Research Station. The majority of blocks in the image would be snow or grey sky and would be encoded as Luma only, and only those containing the brightly colored pixels of the base itself would be encoded as RGB. Similarly, if an image is completely opaque, the encoder should never choose a color endpoint mode which includes alpha, but the convere is not true. In an image with variable opacity, the encoder should pick color endpoints without alpha for opaque areas, and only use LA or RGBA endocing modes for those blocks which are actually semi-transparent.
The swizzle pattern in the encoder just allows you to switch the input or output color channels around, in case your inputs are (for example) encoded in BGR mode. Or are you referring to the swizzle mentioned in HDR Endpoint Mode 7? If so, that ensures that the component with the largest value is in a consistent position in the encoding.
In OpenGL ES, the sRGB conversion happens before the values are handed across to the shader, so the converter must be placed in this position in the pipeline. It is likely that this hardware already exists to service uncompressed sRGB, however, in which case it should not be expensive in terms of area or implementation.
Sean.