gl: Fail if GL implementation doesn't support shaders

The non-shaders implementation was never tuned for fixed-function GL
implementation, the maintainers are not interested in supporting it,
and the hardware is rather rare at this point.  This lets us focus on
the implementation for modern hardware, which needs plenty of work
still.

Reviewed-by: Eric Anholt <eric@anholt.net>

1 files changed, 6 insertions, 0 deletions

diff --git a/src/cairo-gl-shaders.c b/src/cairo-gl-shaders.c
index 2b31bfc75..6a42fd154 100644
--- a/src/cairo-gl-shaders.c
+++ b/src/cairo-gl-shaders.c
@@ -359,9 +359,15 @@ _cairo_gl_context_init_shaders (cairo_gl_context_t *ctx)
 	(_cairo_gl_has_extension ("GL_ARB_shader_objects") &&
 	 _cairo_gl_has_extension ("GL_ARB_fragment_shader") &&
 	 _cairo_gl_has_extension ("GL_ARB_vertex_shader")))
+    {
 	ctx->shader_impl = &shader_impl_core_2_0;
+    }
     else
+    {
 	ctx->shader_impl = NULL;
+	fprintf (stderr, "Error: The cairo gl backend requires shader support!\n");
+	return CAIRO_STATUS_DEVICE_ERROR;
+    }
 
     memset (ctx->vertex_shaders, 0, sizeof (ctx->vertex_shaders));