glamor: check max native ALU instructions

When using glamor (either in Xephyr or Xwayland) on hardware with too
low instructions limit, glamor fallbacks to sw due to large shaders.

This makes glamor unbearably slow on such hardware.

Check reported value for GL_MAX_PROGRAM_NATIVE_ALU_INSTRUCTIONS_ARB
and fail in glamor_init() if the limit is lower than 128.

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=88316
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>

1 files changed, 32 insertions, 0 deletions

diff --git a/glamor/glamor.c b/glamor/glamor.c
index a6d97eadd..6f4f30927 100644
--- a/glamor/glamor.c
+++ b/glamor/glamor.c
@@ -301,6 +301,35 @@ glamor_create_screen_resources(ScreenPtr screen)
     return ret;
 }
 
+static Bool
+glamor_check_instruction_count(int gl_version)
+{
+    GLint max_native_alu_instructions;
+
+    /* Avoid using glamor if the reported instructions limit is too low,
+     * as this would cause glamor to fallback on sw due to large shaders
+     * which ends up being unbearably slow.
+     */
+    if (gl_version < 30) {
+        if (!epoxy_has_gl_extension("GL_ARB_fragment_program")) {
+            ErrorF("GL_ARB_fragment_program required\n");
+            return FALSE;
+        }
+
+        glGetProgramivARB(GL_FRAGMENT_PROGRAM_ARB,
+                          GL_MAX_PROGRAM_NATIVE_ALU_INSTRUCTIONS_ARB,
+                          &max_native_alu_instructions);
+        if (max_native_alu_instructions < GLAMOR_MIN_ALU_INSTRUCTIONS) {
+            LogMessage(X_WARNING,
+                       "glamor requires at least %d instructions (%d reported)\n",
+                       GLAMOR_MIN_ALU_INSTRUCTIONS, max_native_alu_instructions);
+            return FALSE;
+        }
+    }
+
+    return TRUE;
+}
+
 /** Set up glamor for an already-configured GL context. */
 Bool
 glamor_init(ScreenPtr screen, unsigned int flags)
@@ -378,6 +407,9 @@ glamor_init(ScreenPtr screen, unsigned int flags)
             ErrorF("Require OpenGL version 2.1 or later.\n");
             goto fail;
         }
+
+        if (!glamor_check_instruction_count(gl_version))
+            goto fail;
     } else {
         if (gl_version < 20) {
             ErrorF("Require Open GLES2.0 or later.\n");