svga: draw round points when msaa is enabled

See comments for details.  This allows the piglit
ext_framebuffer_multisample-point-smooth test to pass.

Also, test the pipe_rasterizer_state::point_quad_rasterization field
to see if sprite point rasterization is needed because it's possible
for no sprite_coord_enable bits to be set when drawing sprites.

Finally, remove old, stale comments.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>

diff --git a/src/gallium/drivers/svga/svga_pipe_rasterizer.c b/src/gallium/drivers/svga/svga_pipe_rasterizer.c
index bc0acd94625f42487f7df87baa510bce830f7b8d..1dbf5b6debb59eb07e9946fe75038fcfea404b73 100644 (file)
--- a/src/gallium/drivers/svga/svga_pipe_rasterizer.c
+++ b/src/gallium/drivers/svga/svga_pipe_rasterizer.c
@@ -172,25 +172,27 @@ svga_create_rasterizer_state(struct pipe_context *pipe,
    /* need this for draw module. */
    rast->templ = *templ;
 
-   /* light_twoside          - XXX: need fragment shader variant */
-   /* poly_smooth            - XXX: no fallback available */
-   /* poly_stipple_enable    - draw module */
-   /* sprite_coord_enable    - ? */
-   /* point_quad_rasterization - ? */
-   /* point_size_per_vertex  - ? */
-   /* sprite_coord_mode      - ??? */
-   /* flatshade_first        - handled by index translation */
-   /* half_pixel_center      - XXX - viewport code */
-   /* line_width             - draw module */
-   /* fill_cw, fill_ccw      - draw module or index translation */
-
    rast->shademode = svga_translate_flatshade(templ->flatshade);
    rast->cullmode = svga_translate_cullmode(templ->cull_face, templ->front_ccw);
    rast->scissortestenable = templ->scissor;
    rast->multisampleantialias = templ->multisample;
    rast->antialiasedlineenable = templ->line_smooth;
    rast->lastpixel = templ->line_last_pixel;
-   rast->pointsprite = templ->sprite_coord_enable != 0x0;
+   rast->pointsprite = templ->point_quad_rasterization;
+
+   if (rast->templ.multisample) {
+      /* The OpenGL 3.0 spec says points are always drawn as circles when
+       * MSAA is enabled.  Note that our implementation isn't 100% correct,
+       * though.  Our smooth point implementation involves drawing a square,
+       * computing fragment distance from point center, then attenuating
+       * the fragment alpha value.  We should not attenuate alpha if msaa
+       * is enabled.  We should kill fragments entirely outside the circle
+       * and let the GPU compute per-fragment coverage.
+       * But as-is, our implementation gives acceptable results and passes
+       * Piglit's MSAA point smooth test.
+       */
+      rast->templ.point_smooth = TRUE;
+   }
 
    if (templ->point_smooth) {
       /* For smooth points we need to generate fragments for at least