nir: Add ability for shaders to use window space coordinates.

This patch adds a shader_info field that tells the driver to use window
space coordinates for a given vertex shader. It also enables this feature
in radeonsi (the only NIR-capable driver that supported it in TGSI),
and makes tgsi_to_nir aware of it.

Signed-Off-By: Timur Kristóf <timur.kristof@gmail.com>
Tested-by: Andre Heider <a.heider@gmail.com>
Tested-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/compiler/shader_info.h

@@ -149,6 +149,9 @@ typedef struct shader_info {
       struct {
          /* Which inputs are doubles */
          uint64_t double_inputs;
+
+         /* True if the shader writes position in window space coordinates pre-transform */
+         bool window_space_position;
       } vs;
 
       struct {

src/gallium/auxiliary/nir/tgsi_to_nir.c

@@ -1805,6 +1805,8 @@ tgsi_to_nir(const void *tgsi_tokens,
    s->num_uniforms = scan.const_file_max[0] + 1;
    s->num_outputs = scan.file_max[TGSI_FILE_OUTPUT] + 1;
 
+   s->info.vs.window_space_position = scan.properties[TGSI_PROPERTY_VS_WINDOW_SPACE_POSITION];
+
    c->inputs = rzalloc_array(c, struct nir_variable *, s->num_inputs);
    c->outputs = rzalloc_array(c, struct nir_variable *, s->num_outputs);
 

src/gallium/drivers/radeonsi/si_shader_nir.c

@@ -343,6 +343,9 @@ void si_nir_scan_shader(const struct nir_shader *nir,
 	info->properties[TGSI_PROPERTY_NEXT_SHADER] =
 		pipe_shader_type_from_mesa(nir->info.next_stage);
 
+	info->properties[TGSI_PROPERTY_VS_WINDOW_SPACE_POSITION] =
+		nir->info.vs.window_space_position;
+
 	if (nir->info.stage == MESA_SHADER_TESS_CTRL) {
 		info->properties[TGSI_PROPERTY_TCS_VERTICES_OUT] =
 			nir->info.tess.tcs_vertices_out;