intel: check texture formats in intel_validate_framebuffer()

We can't render into any texture format; only certain formats.
Check that render-to-texture's format is renderable in the
intel_validate_framebuffer()

There seems to be a bug somewhere that causes rendering to rgb565 textures
to be corrupted so disallow that for now.  This will be revisted.

src/mesa/drivers/dri/intel/intel_fbo.c

@@ -634,6 +634,7 @@ intel_finish_render_texture(GLcontext * ctx,
 static void
 intel_validate_framebuffer(GLcontext *ctx, struct gl_framebuffer *fb)
 {
+   struct intel_context *intel = intel_context(ctx);
    const struct intel_renderbuffer *depthRb =
       intel_get_renderbuffer(fb, BUFFER_DEPTH);
    const struct intel_renderbuffer *stencilRb =
@@ -645,6 +646,34 @@ intel_validate_framebuffer(GLcontext *ctx, struct gl_framebuffer *fb)
        */
       fb->_Status = GL_FRAMEBUFFER_UNSUPPORTED_EXT;
    }
+
+   /* check that texture color buffers are a format we can render into */
+   {
+      const struct gl_texture_format *supportedFormat;
+      GLuint i;
+
+      /* The texture format we can render into seems to depend on the
+       * screen depth.  There currently seems to be a problem when
+       * rendering into a rgb565 texture when the screen is abgr8888.
+       */
+      if (intel->front_region->cpp == 4)
+         supportedFormat = &_mesa_texformat_argb8888;
+      else 
+         supportedFormat = &_mesa_texformat_rgb565;
+
+      for (i = 0; i < ctx->Const.MaxDrawBuffers; i++) {
+         const struct gl_texture_object *texObj =
+            fb->Attachment[BUFFER_COLOR0 + i].Texture;
+         if (texObj) {
+            const struct gl_texture_image *texImg =
+               texObj->Image[0][texObj->BaseLevel];
+            if (texImg && texImg->TexFormat != supportedFormat) {
+               fb->_Status = GL_FRAMEBUFFER_UNSUPPORTED_EXT;
+               break;
+            }
+         }
+      }
+   }
 }