i965/fs: Assume fragment color clamping is off when precompiling.

Modern applications frequencly use both UNORM buffers and FLOAT buffers
with color clamping disabled.  (FLOAT with clamping explicitly enabled
and SNORM buffers appear to be less common.)  We don't need to emit
saturates in the fragment shader in either of the common cases.

Mesa sets ctx->Color._ClampFragmentColor to false if all the color
buffers are UNORM.  Also, for GL_FIXED_ONLY mode (the default in
legacy OpenGL), it will be false if any FLOAT buffers are bound.
Since the common case is false, that should be our default.

Thanks to Roland Scheidegger for pointing out some faulty logic
in v1 of this patch (unnecessary code and incorrect explanations).

v2: Drop superfluous code and reword commit message.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
index 606a160..741040b 100644 (file)
--- a/src/mesa/drivers/dri/i965/brw_fs.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
@@ -3217,8 +3217,6 @@ brw_fs_precompile(struct gl_context *ctx, struct gl_shader_program *prog)
                                          BRW_FS_VARYING_INPUT_MASK) > 16)
       key.input_slots_valid = fp->Base.InputsRead | VARYING_BIT_POS;
 
-   key.clamp_fragment_color = ctx->API == API_OPENGL_COMPAT;
-
    unsigned sampler_count = _mesa_fls(fp->Base.SamplersUsed);
    for (unsigned i = 0; i < sampler_count; i++) {
       if (fp->Base.ShadowSamplers & (1 << i)) {