From b39e6f33b60ef9bbaf81f320aaca6a440d8a6a8f Mon Sep 17 00:00:00 2001 From: Eric Anholt Date: Wed, 22 Sep 2010 11:47:03 -0700 Subject: glsl: Rework assignments with write_masks to have LHS chan count match RHS. It turns out that most people new to this IR are surprised when an assignment to (say) 3 components on the LHS takes 4 components on the RHS. It also makes for quite strange IR output: (assign (constant bool (1)) (x) (var_ref color) (swiz x (var_ref v) )) (assign (constant bool (1)) (y) (var_ref color) (swiz yy (var_ref v) )) (assign (constant bool (1)) (z) (var_ref color) (swiz zzz (var_ref v) )) But even worse, even we get it wrong, as shown by this line of our current step(float, vec4): (assign (constant bool (1)) (w) (var_ref t) (expression float b2f (expression bool >= (swiz w (var_ref x))(var_ref edge)))) where we try to assign a float to the writemasked-out x channel and don't supply anything for the actual w channel we're writing. Drivers right now just get lucky since ir_to_mesa spams the float value across all the source channels of a vec4. Instead, the RHS will now have a number of components equal to the number of components actually being written. Hopefully this confuses everyone less, and it also makes codegen for a scalar target simpler. Reviewed-by: Kenneth Graunke Reviewed-by: Ian Romanick --- src/glsl/ir.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'src/glsl/ir.h') diff --git a/src/glsl/ir.h b/src/glsl/ir.h index 240e7cd49a..fa246b5e57 100644 --- a/src/glsl/ir.h +++ b/src/glsl/ir.h @@ -646,6 +646,14 @@ public: * For non-vector types in the LHS, this field will be zero. For vector * types, a bit will be set for each component that is written. Note that * for \c vec2 and \c vec3 types only the lower bits will ever be set. + * + * A partially-set write mask means that each enabled channel gets + * the value from a consecutive channel of the rhs. For example, + * to write just .xyw of gl_FrontColor with color: + * + * (assign (constant bool (1)) (xyw) + * (var_ref gl_FragColor) + * (swiz xyw (var_ref color))) */ unsigned write_mask:4; }; -- cgit v1.2.3