gallium/util: fix color clamp for alpha-only formats

Alpha format only contains one channel, but it is placed in the 4th
position, not 1st.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23497>

diff --git a/src/gallium/auxiliary/util/u_helpers.c b/src/gallium/auxiliary/util/u_helpers.c
index 159d31a..d0d610e 100644 (file)
--- a/src/gallium/auxiliary/util/u_helpers.c
+++ b/src/gallium/auxiliary/util/u_helpers.c
@@ -548,9 +548,12 @@ util_clamp_color(enum pipe_format format,
    union pipe_color_union clamp_color = *color;
    int i;
 
-   for (i = 0; i < util_format_get_nr_components(format); i++) {
+   for (i = 0; i < 4; i++) {
       uint8_t bits = util_format_get_component_bits(format, UTIL_FORMAT_COLORSPACE_RGB, i);
 
+      if (!bits)
+         continue;
+
       if (util_format_is_unorm(format))
          clamp_color.ui[i] = _mesa_unorm_to_unorm(clamp_color.ui[i], bits, bits);
       else if (util_format_is_snorm(format))