[Mesa-dev] [PATCH v3 09/28] mesa: Add RGBA to Luminance conversion helpers

[Jason Ekstrand]

On Tue, Dec 9, 2014 at 4:07 AM, Iago Toral Quiroga <itoral at igalia.com>
wrote:
>
> For glReadPixels with a Luminance destination format we compute luminance
> values from RGBA as L=R+G+B. This, however, requires ad-hoc implementation,
> since pack/unpack functions or _mesa_swizzle_and_convert won't do this
> (and thus, neither will _mesa_format_convert). This patch adds helpers
> to do this computation so they can be used to support conversion to
> luminance
> formats.
>
> The current implementation of glReadPixels does this computation as part
> of the span functions in pack.c (see _mesa_pack_rgba_span_float), that do
> this together with other things like type conversion, etc. We do not want
> to use these functions but use _mesa_format_convert instead (later patches
> will remove the color span functions), so we need to extract this
> functionality
> as helpers.
> ---
>  src/mesa/main/pack.c | 63
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  src/mesa/main/pack.h |  9 ++++++++
>  2 files changed, 72 insertions(+)
>
> diff --git a/src/mesa/main/pack.c b/src/mesa/main/pack.c
> index de6ab27..fa4046c 100644
> --- a/src/mesa/main/pack.c
> +++ b/src/mesa/main/pack.c
> @@ -4334,4 +4334,67 @@ _mesa_rebase_rgba_uint(GLuint n, GLuint rgba[][4],
> GLenum baseFormat)
>     }
>  }
>
> +void
> +_mesa_pack_luminance_from_rgba_float(GLuint n, GLfloat rgba[][4],
> +                                     GLvoid *dstAddr, GLenum dst_format,
> +                                     GLbitfield transferOps)
> +{
> +   int i;
> +   GLfloat *dst = (GLfloat *) dstAddr;
> +
> +   switch (dst_format) {
> +   case GL_LUMINANCE:
> +      if (transferOps & IMAGE_CLAMP_BIT) {
> +         for (i = 0; i < n; i++) {
> +            GLfloat sum = rgba[i][RCOMP] + rgba[i][GCOMP] +
> rgba[i][BCOMP];
> +            dst[i] = CLAMP(sum, 0.0F, 1.0F);
> +         }
> +      } else {
> +         for (i = 0; i < n; i++) {
> +            dst[i] = rgba[i][RCOMP] + rgba[i][GCOMP] + rgba[i][BCOMP];
> +         }
> +      }
> +      return;
> +   case GL_LUMINANCE_ALPHA:
> +      if (transferOps & IMAGE_CLAMP_BIT) {
> +         for (i = 0; i < n; i++) {
> +            GLfloat sum = rgba[i][RCOMP] + rgba[i][GCOMP] +
> rgba[i][BCOMP];
> +            dst[2*i] = CLAMP(sum, 0.0F, 1.0F);
> +            dst[2*i+1] = rgba[i][ACOMP];
> +         }
> +      } else {
> +         for (i = 0; i < n; i++) {
> +            dst[2*i] = rgba[i][RCOMP] + rgba[i][GCOMP] + rgba[i][BCOMP];
> +            dst[2*i+1] = rgba[i][ACOMP];
> +         }
> +      }
> +      return;
> +   default:
> +      assert(!"Unsupported format");
> +   }
> +}
> +
> +void
> +_mesa_pack_luminance_from_rgba_integer(GLuint n, GLuint rgba[][4],
> +                                       GLvoid *dstAddr, GLenum dst_format)
> +{
> +   int i;
> +   GLuint *dst = (GLuint *) dstAddr;
> +
> +   switch (dst_format) {
> +   case GL_LUMINANCE:
> +      for (i = 0; i < n; i++) {
> +         dst[i] = rgba[i][RCOMP] + rgba[i][GCOMP] + rgba[i][BCOMP];
>

I know this is getting old, but don't we need to do some clamping here?  If
we do, then we have to handle signed vs. unsigned seperately.  Yeah, that's
annoying.
--Jason


> +      }
> +      return;
> +   case GL_LUMINANCE_ALPHA:
> +      for (i = 0; i < n; i++) {
> +         dst[2*i] = rgba[i][RCOMP] + rgba[i][GCOMP] + rgba[i][BCOMP];
> +         dst[2*i+1] = rgba[i][ACOMP];
> +      }
> +      return;
> +   default:
> +      assert(!"Unsupported format");
> +   }
> +}
>
> diff --git a/src/mesa/main/pack.h b/src/mesa/main/pack.h
> index 2173b65..2783f23 100644
> --- a/src/mesa/main/pack.h
> +++ b/src/mesa/main/pack.h
> @@ -155,4 +155,13 @@ _mesa_rebase_rgba_float(GLuint n, GLfloat rgba[][4],
> GLenum baseFormat);
>  extern void
>  _mesa_rebase_rgba_uint(GLuint n, GLuint rgba[][4], GLenum baseFormat);
>
> +extern void
> +_mesa_pack_luminance_from_rgba_float(GLuint n, GLfloat rgba[][4],
> +                                     GLvoid *dstAddr, GLenum dst_format,
> +                                     GLbitfield transferOps);
> +
> +extern void
> +_mesa_pack_luminance_from_rgba_integer(GLuint n, GLuint rgba[][4],
> +                                       GLvoid *dstAddr, GLenum
> dst_format);
> +
>  #endif
> --
> 1.9.1
>
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