Fix a few polygon offset errors.

1. edge vectors were miscomputed in do_offset_tri()
2. units and scale assignments were transposed in update_clip_state().
3. intel->polygon_offset_scale is the MRD, apply it to offset_units, not the scale factor.

3 files changed, 15 insertions, 23 deletions

diff --git a/src/mesa/clip/clip_pipe_offset.c b/src/mesa/clip/clip_pipe_offset.c
index 35b4e5c079..7129248f7b 100644
--- a/src/mesa/clip/clip_pipe_offset.c
+++ b/src/mesa/clip/clip_pipe_offset.c
@@ -64,6 +64,7 @@ static void offset_begin( struct clip_pipe_stage *stage )
    else
       offset->hw_data_offset = 0;	
 
+   /* note that MRD should have already been applied to the units value */
    offset->units = stage->pipe->draw->state.offset_units;
    offset->scale = stage->pipe->draw->state.offset_scale;
 
@@ -79,31 +80,26 @@ static void do_offset_tri( struct clip_pipe_stage *stage,
 {
    struct offset_stage *offset = offset_stage(stage);
    GLuint hw_data_offset = offset->hw_data_offset;
-   
+
    GLfloat inv_det = 1.0 / header->det;
 
    GLfloat *v0 = (GLfloat *)&(header->v[0]->data[hw_data_offset]);
    GLfloat *v1 = (GLfloat *)&(header->v[1]->data[hw_data_offset]);
    GLfloat *v2 = (GLfloat *)&(header->v[2]->data[hw_data_offset]);
    
-   GLfloat ex = v0[0] - v2[2];
-   GLfloat fx = v1[0] - v2[2];
-   GLfloat ey = v0[1] - v2[2];
-   GLfloat fy = v1[1] - v2[2];
+   GLfloat ex = v0[0] - v2[0];
+   GLfloat ey = v0[1] - v2[1];
    GLfloat ez = v0[2] - v2[2];
+   GLfloat fx = v1[0] - v2[0];
+   GLfloat fy = v1[1] - v2[1];
    GLfloat fz = v1[2] - v2[2];
 
    GLfloat a = ey*fz - ez*fy;
    GLfloat b = ez*fx - ex*fz;
 
-   GLfloat ac = a * inv_det;
-   GLfloat bc = b * inv_det;
-   GLfloat zoffset;
-
-   if ( ac < 0.0f ) ac = -ac;
-   if ( bc < 0.0f ) bc = -bc;
-
-   zoffset = offset->units + MAX2( ac, bc ) * offset->scale;
+   GLfloat dzdx = FABSF(a * inv_det);
+   GLfloat dzdy = FABSF(b * inv_det);
+   GLfloat zoffset = offset->units + MAX2( dzdx, dzdy ) * offset->scale;
 
    v0[2] += zoffset;
    v1[2] += zoffset;
diff --git a/src/mesa/drivers/dri/i915tex/intel_context.c b/src/mesa/drivers/dri/i915tex/intel_context.c
index 5a0f5f70ec..e852a430e8 100644
--- a/src/mesa/drivers/dri/i915tex/intel_context.c
+++ b/src/mesa/drivers/dri/i915tex/intel_context.c
@@ -485,7 +485,9 @@ intelInitContext(struct intel_context *intel,
 
    /* XXX FBO: recalculate on bind */
    switch (mesaVis->depthBits) {
-   case 0:                     /* what to do in this case? */
+   case 0:
+      intel->polygon_offset_scale = 0.0;
+      break;
    case 16:
       intel->polygon_offset_scale = 1.0 / 0xffff;
       break;
diff --git a/src/mesa/drivers/dri/i915tex/intel_state_clip.c b/src/mesa/drivers/dri/i915tex/intel_state_clip.c
index c91e6654aa..fde54f8f13 100644
--- a/src/mesa/drivers/dri/i915tex/intel_state_clip.c
+++ b/src/mesa/drivers/dri/i915tex/intel_state_clip.c
@@ -137,24 +137,18 @@ static void update_clip_state( struct intel_context *intel )
    if (state.fill_cw != FILL_TRI)
       state.offset_cw = get_offset_flag( state.fill_cw, 
 					 intel->state.Polygon );
-   
    if (state.fill_ccw != FILL_TRI)
       state.offset_ccw = get_offset_flag( state.fill_ccw, 
 					  intel->state.Polygon );
 
-
    /* _NEW_BUFFERS, _NEW_POLYGON
     */
    if (state.fill_cw != FILL_TRI ||
        state.fill_ccw != FILL_TRI)
    {
-      GLfloat mrd = (intel->state.DrawBuffer ? 
-		     intel->state.DrawBuffer->_MRD : 
-		     1.0);
-
-      state.offset_units = intel->state.Polygon->OffsetFactor * mrd;
-      state.offset_scale = (intel->state.Polygon->OffsetUnits * mrd *
-			    intel->polygon_offset_scale);
+      GLfloat mrd = intel->polygon_offset_scale;
+      state.offset_scale = intel->state.Polygon->OffsetFactor;
+      state.offset_units = intel->state.Polygon->OffsetUnits * mrd;
    }