1 files changed, 29 insertions, 11 deletions

diff --git a/source/blender/gpu/shaders/gpu_shader_3D_polyline_geom.glsl b/source/blender/gpu/shaders/gpu_shader_3D_polyline_geom.glsl
index b28205b349e..fd9b7e221e6 100644
--- a/source/blender/gpu/shaders/gpu_shader_3D_polyline_geom.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_3D_polyline_geom.glsl
@@ -20,13 +20,30 @@ noperspective out float smoothline;
 
 #define SMOOTH_WIDTH 1.0
 
-void do_vertex(const int i, vec2 ofs)
+/* Clips point to near clip plane before perspective divide. */
+vec4 clip_line_point_homogeneous_space(vec4 p, vec4 q)
+{
+  if (p.z < -p.w) {
+    /* Just solves p + (q - p) * A; for A when p.z / p.w = -1.0. */
+    float denom = q.z - p.z + q.w - p.w;
+    if (denom == 0.0) {
+      /* No solution. */
+      return p;
+    }
+    float A = (-p.z - p.w) / denom;
+    p = p + (q - p) * A;
+  }
+  return p;
+}
+
+void do_vertex(const int i, vec4 pos, vec2 ofs)
 {
 #if defined(UNIFORM)
   finalColor = color;
 
 #elif defined(FLAT)
-  finalColor = finalColor_g[0];
+  /* WATCH: Assuming last provoking vertex. */
+  finalColor = finalColor_g[1];
 
 #elif defined(SMOOTH)
   finalColor = finalColor_g[i];
@@ -37,21 +54,22 @@ void do_vertex(const int i, vec2 ofs)
 #endif
 
   smoothline = (lineWidth + SMOOTH_WIDTH) * 0.5;
-  gl_Position = gl_in[i].gl_Position;
-  gl_Position.xy += ofs * gl_Position.w;
+  gl_Position = pos;
+  gl_Position.xy += ofs * pos.w;
   EmitVertex();
 
   smoothline = -(lineWidth + SMOOTH_WIDTH) * 0.5;
-  gl_Position = gl_in[i].gl_Position;
-  gl_Position.xy -= ofs * gl_Position.w;
+  gl_Position = pos;
+  gl_Position.xy -= ofs * pos.w;
   EmitVertex();
 }
 
 void main(void)
 {
-  vec2 p0 = gl_in[0].gl_Position.xy / gl_in[0].gl_Position.w;
-  vec2 p1 = gl_in[1].gl_Position.xy / gl_in[1].gl_Position.w;
-  vec2 e = normalize((p1 - p0) * viewportSize.xy);
+  vec4 p0 = clip_line_point_homogeneous_space(gl_in[0].gl_Position, gl_in[1].gl_Position);
+  vec4 p1 = clip_line_point_homogeneous_space(gl_in[1].gl_Position, gl_in[0].gl_Position);
+  vec2 e = normalize(((p1.xy / p1.w) - (p0.xy / p0.w)) * viewportSize.xy);
+
 #if 0 /* Hard turn when line direction changes quadrant. */
   e = abs(e);
   vec2 ofs = (e.x > e.y) ? vec2(0.0, 1.0 / e.x) : vec2(1.0 / e.y, 0.0);
@@ -61,8 +79,8 @@ void main(void)
   ofs /= viewportSize.xy;
   ofs *= lineWidth + SMOOTH_WIDTH;
 
-  do_vertex(0, ofs);
-  do_vertex(1, ofs);
+  do_vertex(0, p0, ofs);
+  do_vertex(1, p1, ofs);
 
   EndPrimitive();
 }