Kenneth Graunke <kenn...@whitecape.org> writes:
> When considering color write masks, we often want to know whether an
> RGBA component actually contains any meaningful data. This function
> provides an easy way to answer that question, and handles luminance,
> intensity, and alpha formats correctly.
>
> Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
> ---
> src/mesa/main/formats.c | 29 +++++++++++++++++++++++++++++
> src/mesa/main/formats.h | 4 ++++
> 2 files changed, 33 insertions(+)
>
> diff --git a/src/mesa/main/formats.c b/src/mesa/main/formats.c
> index c3e8049..4fb1f11 100644
> --- a/src/mesa/main/formats.c
> +++ b/src/mesa/main/formats.c
> @@ -2207,6 +2207,35 @@ _mesa_format_num_components(mesa_format format)
>
>
> /**
> + * Returns true if a color format has data stored in the R/G/B/A channels,
> + * given an index from 0 to 3.
> + */
> +bool
> +_mesa_format_has_color_component(mesa_format format, int component)
> +{
> + const struct gl_format_info *info = _mesa_get_format_info(format);
> +
> + assert(info->BaseFormat != GL_DEPTH_COMPONENT &&
> + info->BaseFormat != GL_DEPTH_STENCIL &&
> + info->BaseFormat != GL_STENCIL_INDEX);
> +
> + switch (component) {
> + case 0:
> + return (info->RedBits + info->IntensityBits + info->LuminanceBits) > 0;
> + case 1:
> + return (info->GreenBits + info->IntensityBits + info->LuminanceBits) >
> 0;
> + case 2:
> + return (info->BlueBits + info->IntensityBits + info->LuminanceBits) >
> 0;
> + case 3:
> + return (info->AlphaBits + info->IntensityBits) > 0;
> + default:
> + assert(!"Invalid color component: must be 0..3");
> + return false;
> + }
> +}It would be possible to catch more cases by having the BaseFormat passed in from the outseide, so we'd answer false when asked about the A channel of an RGB texture that got stored in an ARGB mesa_format. However, this all appears correct now, and it's a big win, so the series is: Reviewed-by: Eric Anholt <e...@anholt.net>
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