gallium: add a new cap PIPE_CAP_GLSL_ZERO_INIT

Allows driver to select a zero init mode between the 3 possible values.

Reviewed-by: Marek Olšák <[email protected]>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4607>

2 files changed, 8 insertions, 2 deletions

diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index 7046e8adfa3..2fa06e7a570 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -3868,9 +3868,13 @@ struct gl_constants
    GLboolean ForceGLSLAbsSqrt;
 
    /**
-    * Types of variable to default initialized to zero.
+    * Types of variable to default initialized to zero. Supported values are:
+    *   - 0: no zero initialization
+    *   - 1: all shader variables and gl_FragColor are initialiazed to 0
+    *   - 2: same as 1, but shader out variables are *not* initialized, while
+    *        function out variables are now initialized.
     */
-   GLuint GLSLZeroInit;
+   GLchar GLSLZeroInit;
 
    /**
     * Treat integer textures using GL_LINEAR filters as GL_NEAREST.
diff --git a/src/mesa/state_tracker/st_extensions.c b/src/mesa/state_tracker/st_extensions.c
index 2403bd60a8c..f13ded7c19d 100644
--- a/src/mesa/state_tracker/st_extensions.c
+++ b/src/mesa/state_tracker/st_extensions.c
@@ -1205,6 +1205,8 @@ void st_init_extensions(struct pipe_screen *screen,
 
    if (options->glsl_zero_init) {
       consts->GLSLZeroInit = 1;
+   } else {
+      consts->GLSLZeroInit = screen->get_param(screen, PIPE_CAP_GLSL_ZERO_INIT);
    }
 
    consts->ForceIntegerTexNearest = options->force_integer_tex_nearest;