[Mesa-dev] [PATCH] mesa: add special case ubyte[4] / BGRA conversion function

[Roland Scheidegger]

Looks ok to me, albeit the sse2 code I posted a while ago for handling
swizzled stores probably would be faster still (though only with x86
sse2...). At least I think it would hit this (if not the next patch in
the series should...).
Matt Turner reviewed the first 2 patches in the series (albeit I had to
revert the second one due to a crash bug in i965 which was hiding behind
a __SSE3__ ifdef before...) but the others are unreviewed (honestly, I'm
not fully convinced of the approach neither...).

https://lists.freedesktop.org/archives/mesa-dev/2016-January/105116.html

Roland


Am 18.02.2016 um 16:52 schrieb Brian Paul:
> This reduces a glTexImage(GL_RGBA, GL_UNSIGNED_BYTE) hot spot in when
> storing the texture as BGRA.
> ---
>  src/mesa/main/format_utils.c | 74 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 69 insertions(+), 5 deletions(-)
> 
> diff --git a/src/mesa/main/format_utils.c b/src/mesa/main/format_utils.c
> index 5fdabd5..d16d69c 100644
> --- a/src/mesa/main/format_utils.c
> +++ b/src/mesa/main/format_utils.c
> @@ -179,6 +179,63 @@ _mesa_compute_rgba2base2rgba_component_mapping(GLenum baseFormat, uint8_t *map)
>     }
>  }
>  
> +
> +/**
> + * Special case conversion function to swap r/b channels from the source
> + * image to the dest image.
> + */
> +static void
> +convert_ubyte_rgba_to_bgra(size_t width, size_t height,
> +                           const uint8_t *src, size_t src_stride,
> +                           uint8_t *dst, size_t dst_stride)
> +{
> +   int row;
> +
> +   if (sizeof(void *) == 8 &&
> +       src_stride % 8 == 0 &&
> +       dst_stride % 8 == 0 &&
> +       (GLsizeiptr) src % 8 == 0 &&
> +       (GLsizeiptr) dst % 8 == 0) {
> +      /* use 64-bit word to swizzle two 32-bit pixels.  We need 8-byte
> +       * alignment for src/dst addresses and strides.
> +       */
> +      for (row = 0; row < height; row++) {
> +         const GLuint64 *s = (const GLuint64 *) src;
> +         GLuint64 *d = (GLuint64 *) dst;
> +         int i;
> +         for (i = 0; i < width/2; i++) {
> +            d[i] = ( (s[i] & 0xff00ff00ff00ff00) |
> +                    ((s[i] &       0xff000000ff) << 16) |
> +                    ((s[i] &   0xff000000ff0000) >> 16));
> +         }
> +         if (width & 1) {
> +            /* handle the case of odd widths */
> +            const GLuint s = ((const GLuint *) src)[width - 1];
> +            GLuint *d = (GLuint *) dst + width - 1;
> +            *d = ( (s & 0xff00ff00) |
> +                  ((s &       0xff) << 16) |
> +                  ((s &   0xff0000) >> 16));
> +         }
> +         src += src_stride;
> +         dst += dst_stride;
> +      }
> +   } else {
> +      for (row = 0; row < height; row++) {
> +         const GLuint *s = (const GLuint *) src;
> +         GLuint *d = (GLuint *) dst;
> +         int i;
> +         for (i = 0; i < width; i++) {
> +            d[i] = ( (s[i] & 0xff00ff00) |
> +                    ((s[i] &       0xff) << 16) |
> +                    ((s[i] &   0xff0000) >> 16));
> +         }
> +         src += src_stride;
> +         dst += dst_stride;
> +      }
> +   }
> +}
> +
> +
>  /**
>   * This can be used to convert between most color formats.
>   *
> @@ -299,11 +356,18 @@ _mesa_format_convert(void *void_dst, uint32_t dst_format, size_t dst_stride,
>              return;
>           } else if (src_array_format == RGBA8_UBYTE) {
>              assert(!_mesa_is_format_integer_color(dst_format));
> -            for (row = 0; row < height; ++row) {
> -               _mesa_pack_ubyte_rgba_row(dst_format, width,
> -                                         (const uint8_t (*)[4])src, dst);
> -               src += src_stride;
> -               dst += dst_stride;
> +
> +            if (dst_format == MESA_FORMAT_B8G8R8A8_UNORM) {
> +               convert_ubyte_rgba_to_bgra(width, height, src, src_stride,
> +                                          dst, dst_stride);
> +            }
> +            else {
> +               for (row = 0; row < height; ++row) {
> +                  _mesa_pack_ubyte_rgba_row(dst_format, width,
> +                                            (const uint8_t (*)[4])src, dst);
> +                  src += src_stride;
> +                  dst += dst_stride;
> +               }
>              }
>              return;
>           } else if (src_array_format == RGBA32_UINT &&
>