svga: use dummy shaders when translation fails

Before, if shader translation failed for any reason we'd keep trying
to translate the shader over and over again during state validation.
The dummy fragment shader emits solid red so that might be visual
clue that translation is failing.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

1 files changed, 47 insertions, 2 deletions

diff --git a/src/gallium/drivers/svga/svga_state_vs.c b/src/gallium/drivers/svga/svga_state_vs.c
index b82e685..3cb0cdb 100644
--- a/src/gallium/drivers/svga/svga_state_vs.c
+++ b/src/gallium/drivers/svga/svga_state_vs.c
@@ -27,8 +27,10 @@
 #include "pipe/p_defines.h"
 #include "util/u_format.h"
 #include "util/u_math.h"
+#include "util/u_memory.h"
 #include "util/u_bitmask.h"
 #include "translate/translate.h"
+#include "tgsi/tgsi_ureg.h"
 
 #include "svga_context.h"
 #include "svga_state.h"
@@ -65,6 +67,37 @@ static struct svga_shader_result *search_vs_key( struct svga_vertex_shader *vs,
 }
 
 
+/**
+ * If we fail to compile a vertex shader we'll use a dummy/fallback shader
+ * that simply emits a (0,0,0,1) vertex position.
+ */
+static const struct tgsi_token *
+get_dummy_vertex_shader(void)
+{
+   static const float zero[4] = { 0.0, 0.0, 0.0, 1.0 };
+   struct ureg_program *ureg;
+   const struct tgsi_token *tokens;
+   struct ureg_src src;
+   struct ureg_dst dst;
+   unsigned num_tokens;
+
+   ureg = ureg_create(TGSI_PROCESSOR_VERTEX);
+   if (!ureg)
+      return NULL;
+
+   dst = ureg_DECL_output(ureg, TGSI_SEMANTIC_POSITION, 0);
+   src = ureg_DECL_immediate(ureg, zero, 4);
+   ureg_MOV(ureg, dst, src);
+   ureg_END(ureg);
+
+   tokens = ureg_get_tokens(ureg, &num_tokens);
+
+   ureg_destroy(ureg);
+
+   return tokens;
+}
+
+
 static enum pipe_error compile_vs( struct svga_context *svga,
                                    struct svga_vertex_shader *vs,
                                    const struct svga_vs_compile_key *key,
@@ -75,8 +108,20 @@ static enum pipe_error compile_vs( struct svga_context *svga,
 
    result = svga_translate_vertex_program( vs, key );
    if (result == NULL) {
-      ret = PIPE_ERROR_OUT_OF_MEMORY;
-      goto fail;
+      /* some problem during translation, try the dummy shader */
+      const struct tgsi_token *dummy = get_dummy_vertex_shader();
+      if (!dummy) {
+         ret = PIPE_ERROR_OUT_OF_MEMORY;
+         goto fail;
+      }
+      debug_printf("Failed to compile vertex shader, using dummy shader instead.\n");
+      FREE((void *) vs->base.tokens);
+      vs->base.tokens = dummy;
+      result = svga_translate_vertex_program(vs, key);
+      if (result == NULL) {
+         ret = PIPE_ERROR;
+         goto fail;
+      }
    }
 
    result->id = util_bitmask_add(svga->vs_bm);