[Mesa-dev] [PATCH 04/30] i965: Clamp clear colors to the representable range

[Jason Ekstrand]

Starting with Sky Lake, we can clear to arbitrary floats or integers.
Unfortunately, the hardware isn't particularly smart when it comes
sampling from that clear color.  If the clear color is out of range for
the surface format, it will happily return whatever we put in the
surface state packet unmodified.  In order to avoid returning bogus
values for surfaces with a limited range, we need to do some clamping.

Cc: "17.1" <mesa-stable at lists.freedesktop.org>
---
 src/mesa/drivers/dri/i965/brw_meta_util.c | 40 +++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_meta_util.c b/src/mesa/drivers/dri/i965/brw_meta_util.c
index 2416079..3751785 100644
--- a/src/mesa/drivers/dri/i965/brw_meta_util.c
+++ b/src/mesa/drivers/dri/i965/brw_meta_util.c
@@ -364,6 +364,46 @@ brw_meta_convert_fast_clear_color(const struct brw_context *brw,
       break;
    }
 
+   switch (_mesa_get_format_datatype(mt->format)) {
+   case GL_UNSIGNED_NORMALIZED:
+      for (int i = 0; i < 4; i++)
+         override_color.f32[i] = CLAMP(override_color.f32[i], 0.0f, 1.0f);
+      break;
+
+   case GL_SIGNED_NORMALIZED:
+      for (int i = 0; i < 4; i++)
+         override_color.f32[i] = CLAMP(override_color.f32[i], -1.0f, 1.0f);
+      break;
+
+   case GL_UNSIGNED_INT:
+      for (int i = 0; i < 4; i++) {
+         unsigned bits = _mesa_get_format_bits(mt->format, GL_RED_BITS + i);
+         if (bits < 32) {
+            uint32_t max = (1u << bits) - 1;
+            override_color.u32[i] = MIN2(override_color.u32[i], max);
+         }
+      }
+      break;
+
+   case GL_INT:
+      for (int i = 0; i < 4; i++) {
+         unsigned bits = _mesa_get_format_bits(mt->format, GL_RED_BITS + i);
+         if (bits < 32) {
+            int32_t max = (1 << (bits - 1)) - 1;
+            int32_t min = -(1 << (bits - 1));
+            override_color.i32[i] = CLAMP(override_color.i32[i], min, max);
+         }
+      }
+      break;
+
+   case GL_FLOAT:
+      if (!_mesa_is_format_signed(mt->format)) {
+         for (int i = 0; i < 4; i++)
+            override_color.f32[i] = MAX2(override_color.f32[i], 0.0f);
+      }
+      break;
+   }
+
    if (!_mesa_format_has_color_component(mt->format, 3)) {
       if (_mesa_is_format_integer_color(mt->format))
          override_color.u32[3] = 1;
-- 
2.5.0.400.gff86faf