draw: fix broken polygon offset stage

There were several issues.  We weren't handling different front/back
polygon fill modes.  We weren't checking whether the offset applied to
fill mode vs. line mode vs. point mode.

Fixes problems found with the Visualization Toolkit (VTK) test suite.

Note: This is a candidate for the stable branches.

Reviewed-by: Jose Fonseca <jfonseca@vmware.com>
(cherry picked from commit d6b8b116eec3c24ef9f2d292315f70ea8cbaa040)

1 files changed, 37 insertions, 3 deletions

diff --git a/src/gallium/auxiliary/draw/draw_pipe_offset.c b/src/gallium/auxiliary/draw/draw_pipe_offset.c
index 3da52b1062..3578525051 100644
--- a/src/gallium/auxiliary/draw/draw_pipe_offset.c
+++ b/src/gallium/auxiliary/draw/draw_pipe_offset.c
@@ -127,10 +127,44 @@ static void offset_first_tri( struct draw_stage *stage,
 			      struct prim_header *header )
 {
    struct offset_stage *offset = offset_stage(stage);
+   const struct pipe_rasterizer_state *rast = stage->draw->rasterizer;
+   unsigned fill_mode = rast->fill_front;
+   boolean do_offset;
+
+   if (rast->fill_back != rast->fill_front) {
+      /* Need to check for back-facing triangle */
+      boolean ccw = header->det < 0.0f;
+      if (ccw != rast->front_ccw)
+         fill_mode = rast->fill_back;
+   }
+
+   /* Now determine if we need to do offsetting for the point/line/fill mode */
+   switch (fill_mode) {
+   case PIPE_POLYGON_MODE_FILL:
+      do_offset = rast->offset_tri;
+      break;
+   case PIPE_POLYGON_MODE_LINE:
+      do_offset = rast->offset_line;
+      break;
+   case PIPE_POLYGON_MODE_POINT:
+      do_offset = rast->offset_point;
+      break;
+   default:
+      assert(!"invalid fill_mode in offset_first_tri()");
+      do_offset = rast->offset_tri;
+   }
+
+   if (do_offset) {
+      offset->scale = rast->offset_scale;
+      offset->clamp = rast->offset_clamp;
+      offset->units = (float) (rast->offset_units * stage->draw->mrd);
+   }
+   else {
+      offset->scale = 0.0f;
+      offset->clamp = 0.0f;
+      offset->units = 0.0f;
+   }
 
-   offset->units = (float) (stage->draw->rasterizer->offset_units * stage->draw->mrd);
-   offset->scale = stage->draw->rasterizer->offset_scale;
-   offset->clamp = stage->draw->rasterizer->offset_clamp;
 
    stage->tri = offset_tri;
    stage->tri( stage, header );