[Bf-blender-cvs] [efb20da] master: Fix T43735 painting on perpendicular to the screen polygons is problematic (still!)

[Antony Riakiotakis]

Commit: efb20dacc6561cee831f1dfc546ef33083d4df80
Author: Antony Riakiotakis
Date:   Thu Feb 19 16:38:56 2015 +0100
Branches: master
https://developer.blender.org/rBefb20dacc6561cee831f1dfc546ef33083d4df80

Fix T43735 painting on perpendicular to the screen polygons is
problematic (still!)

It seems due to floating point precision issues we have to account for
even more cases.

Added colinear check for one more triangle edge-vertex and assumed that
if no collision test is found then triangle is completely inside box.

Such cases are mostly from float precision not catching triangle just
outside bucket. Now tests are much better for simple tests (paint/flood
fill cube from ortho view, paint sphere), however there are still some
rare cases of stray pixels.

===================================================================

M	source/blender/editors/sculpt_paint/paint_image_proj.c

===================================================================

diff --git a/source/blender/editors/sculpt_paint/paint_image_proj.c b/source/blender/editors/sculpt_paint/paint_image_proj.c
index cce5c2c..15a65cd 100644
--- a/source/blender/editors/sculpt_paint/paint_image_proj.c
+++ b/source/blender/editors/sculpt_paint/paint_image_proj.c
@@ -1997,7 +1997,7 @@ static int float_z_sort(const void *p1, const void *p2)
 }
 
 /* assumes one point is within the rectangle */
-static void line_rect_clip(
+static bool line_rect_clip(
         const rctf *rect,
         const float l1[4], const float l2[4],
         const float uv1[2], const float uv2[2],
@@ -2021,10 +2021,16 @@ static void line_rect_clip(
 		min = min_ff((tmp - l1[1]) / (l2[1] - l1[1]), min);
 	}
 	
+	/* it's rare but it can happen if l1 == l2 */
+	if (min == FLT_MAX)
+		return false;
+
 	tmp = (is_ortho) ? 1.0f : (l1[3] + min * (l2[3] - l1[3]));
-	
+
 	uv[0] = (uv1[0] + min / tmp * (uv2[0] - uv1[0]));
 	uv[1] = (uv1[1] + min / tmp * (uv2[1] - uv1[1]));
+
+	return true;
 }
 
 
@@ -2045,8 +2051,9 @@ static void project_bucket_clip_face(
 	float bucket_bounds_ss[4][2];
 
 	/* detect pathological case where face the three vertices are almost colinear in screen space.
-	 * mostly those will be culled but when flood filling or with smooth shading */
-	if (dist_squared_to_line_v2(v1coSS, v2coSS, v3coSS) < PROJ_PIXEL_TOLERANCE)
+	 * mostly those will be culled but when flood filling or with smooth shading it's a possibility */
+	if (dist_squared_to_line_v2(v1coSS, v2coSS, v3coSS) < 0.5f ||
+		dist_squared_to_line_v2(v2coSS, v3coSS, v1coSS) < 0.5f)
 		colinear = true;
 	
 	/* get the UV space bounding box */
@@ -2084,28 +2091,34 @@ static void project_bucket_clip_face(
 
 		flag = inside_bucket_flag & (ISECT_1 | ISECT_2);
 		if (flag && flag != (ISECT_1 | ISECT_2)) {
-			line_rect_clip(bucket_bounds, v1coSS, v2coSS, uv1co, uv2co, bucket_bounds_uv[*tot], is_ortho);
-			(*tot)++;
+			if (line_rect_clip(bucket_bounds, v1coSS, v2coSS, uv1co, uv2co, bucket_bounds_uv[*tot], is_ortho))
+				(*tot)++;
 		}
 		
 		if (inside_bucket_flag & ISECT_2) { copy_v2_v2(bucket_bounds_uv[*tot], uv2co); (*tot)++; }
 		
 		flag = inside_bucket_flag & (ISECT_2 | ISECT_3);
 		if (flag && flag != (ISECT_2 | ISECT_3)) {
-			line_rect_clip(bucket_bounds, v2coSS, v3coSS, uv2co, uv3co, bucket_bounds_uv[*tot], is_ortho);
-			(*tot)++;
+			if (line_rect_clip(bucket_bounds, v2coSS, v3coSS, uv2co, uv3co, bucket_bounds_uv[*tot], is_ortho))
+				(*tot)++;
 		}
 
 		if (inside_bucket_flag & ISECT_3) { copy_v2_v2(bucket_bounds_uv[*tot], uv3co); (*tot)++; }
 
 		flag = inside_bucket_flag & (ISECT_3 | ISECT_1);
 		if (flag && flag != (ISECT_3 | ISECT_1)) {
-			line_rect_clip(bucket_bounds, v3coSS, v1coSS, uv3co, uv1co, bucket_bounds_uv[*tot], is_ortho);
-			(*tot)++;
+			if (line_rect_clip(bucket_bounds, v3coSS, v1coSS, uv3co, uv1co, bucket_bounds_uv[*tot], is_ortho))
+				(*tot)++;
 		}
 		
-		if ((*tot) < 3) { /* no intersections to speak of */
+		if ((*tot) < 3) {
+			/* no intersections to speak of, but more probable is that all face is just outside the
+			 * rectangle and culled due to float precision issues. Since above teste have failed,
+			 * just dump triangle as is for painting */
 			*tot = 0;
+			copy_v2_v2(bucket_bounds_uv[*tot], uv1co); (*tot)++;
+			copy_v2_v2(bucket_bounds_uv[*tot], uv2co); (*tot)++;
+			copy_v2_v2(bucket_bounds_uv[*tot], uv3co); (*tot)++;
 			return;
 		}