[Mesa-dev] [PATCH 4/5] mesa: Add function for decoding ETC1 textures

[Kenneth Graunke]

On 07/09/2012 10:46 AM, Chad Versace wrote:
> Add function _mesa_etc1_image_decode_to_abgr8888(). It is intended to be
> used by glCompressedTexSubImage2D to translate ETC1 textures into ABGR.
> 
> Signed-off-by: Chad Versace <chad.versace at linux.intel.com>
> ---
>  src/mesa/main/texcompress_etc.c | 82 +++++++++++++++++++++++++++++++++++++++++
>  src/mesa/main/texcompress_etc.h |  6 +++
>  2 files changed, 88 insertions(+)
> 
> diff --git a/src/mesa/main/texcompress_etc.c b/src/mesa/main/texcompress_etc.c
> index e3b2e83..d84ee0e 100644
> --- a/src/mesa/main/texcompress_etc.c
> +++ b/src/mesa/main/texcompress_etc.c
> @@ -178,3 +178,85 @@ _mesa_fetch_texel_2d_f_etc1_rgb8(const struct swrast_texture_image *texImage,
>     texel[BCOMP] = UBYTE_TO_FLOAT(bgr888[2]);
>     texel[ACOMP] = 1.0f;
>  }
> +
> +static int
> +align(int x, int m)
> +{
> +   return (m * x + m - 1) / m;
> +}

Perhaps we should just move the ALIGN and ROUND_DOWN_TO macros from
intel_context.h into macros.h?

For reference, ALIGN() is:
#define ALIGN(value, alignment)  (((value) + alignment - 1) &
~(alignment - 1))

Either way, this patch looks right to me.
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

> +
> +/**
> + * Decode texture data in format `MESA_FORMAT_ETC1_RGB8` to
> + * `MESA_FORMAT_ABGR8888`.
> + *
> + * The size of the source data must be a multiple of the ETC1 block size,
> + * which is 8, even if the texture image's dimensions are not aligned to 4.
> + * From the GL_OES_compressed_ETC1_RGB8_texture spec:
> + *   The texture is described as a number of 4x4 pixel blocks. If the
> + *   texture (or a particular mip-level) is smaller than 4 pixels in
> + *   any dimension (such as a 2x2 or a 8x1 texture), the texture is
> + *   found in the upper left part of the block(s), and the rest of the
> + *   pixels are not used. For instance, a texture of size 4x2 will be
> + *   placed in the upper half of a 4x4 block, and the lower half of the
> + *   pixels in the block will not be accessed.
> + *
> + * \param src_width in pixels
> + * \param src_height in pixels
> + * \param dst_rowstride in bytes
> + */
> +void
> +_mesa_etc1_image_decode_to_abgr8888(const uint8_t *src,
> +                                    int src_width,
> +                                    int src_height,
> +                                    uint8_t *dst,
> +                                    int dst_rowstride)
> +{
> +   /* An XRGB pixel is 4 bytes. */
> +   const int pixel_bytes = 4;
> +
> +   /* A block contains 4x4 pixels. */
> +   const int block_width = 4;
> +   const int block_height = 4;
> +
> +   /* A block contains 8 bytes. */
> +   const int block_bytes = 8;
> +
> +   /* The stride in units of blocks. */
> +   const int block_stride = align(src_width, block_width) / block_width;
> +
> +   /* The block being decoded. */
> +   int block_x;
> +   int block_y;
> +
> +   /* Iterate over each block. */
> +   for (block_y = 0; block_y * block_height < src_height; ++block_y) {
> +      for (block_x = 0; block_x * block_width < src_width; ++block_x) {
> +         struct etc1_block block;
> +
> +         /* The pixel's position relative to the block's base. */
> +         int pixel_x;
> +         int pixel_y;
> +
> +         const uint8_t *src_block_base =
> +               src + block_bytes * (block_y * block_stride + block_x);
> +
> +         uint8_t *dst_block_base = dst
> +                                 + block_y * block_height * dst_rowstride
> +                                 + block_x * block_width * pixel_bytes;
> +
> +         etc1_parse_block(&block, src_block_base);
> +
> +         /* Iterate over each pixel in block. */
> +         for (pixel_y = 0; pixel_y < block_height; ++pixel_y) {
> +            for (pixel_x = 0; pixel_x < block_width; ++pixel_x) {
> +               uint8_t *dst_texel = dst_block_base
> +                                  + pixel_y * dst_rowstride
> +                                  + pixel_x * pixel_bytes;
> +
> +               etc1_fetch_texel(&block, pixel_x, pixel_y, dst_texel);
> +               dst_texel[3] = 0xff;
> +            }
> +         }
> +      }
> +   }
> +}
> diff --git a/src/mesa/main/texcompress_etc.h b/src/mesa/main/texcompress_etc.h
> index 8e8427f..552a7bd 100644
> --- a/src/mesa/main/texcompress_etc.h
> +++ b/src/mesa/main/texcompress_etc.h
> @@ -36,5 +36,11 @@ _mesa_texstore_etc1_rgb8(TEXSTORE_PARAMS);
>  void
>  _mesa_fetch_texel_2d_f_etc1_rgb8(const struct swrast_texture_image *texImage,
>                                   GLint i, GLint j, GLint k, GLfloat *texel);
> +void
> +_mesa_etc1_image_decode_to_abgr8888(const uint8_t *src,
> +                                    int src_width,
> +                                    int src_height,
> +                                    uint8_t *dst,
> +                                    int dst_rowstride);
>  
>  #endif
>