From c3ed2ee0312d163685e3e8c4d9bbeb3654c27ca7 Mon Sep 17 00:00:00 2001
From: lecoanet
Date: Thu, 26 Sep 2002 10:07:15 +0000
Subject: 	* (ZnRenderPolyline, 	   ZnRenderPolygonRelief): line_width
 doit �tre flottant. Corrige 	un bug erratique de curve trop �paisse quand
 on met 0.5 comme 	�paisseur.         * (ZnRenderPolyline): Corrig�
 (contourn�) le probl�me des cracks 	dans le raccordement des segments d'un
 curve, arc, etc qui 	apparaissaient dans le dessin openGL depuis les
 GeForce 3 et 4. 	C'est li� au rendu des lignes antialias�e et d�pendant
 de la 	quantit� de couverture des pixels de bordures. Pour �tre safe 	on
 antialiase que les lignes compl�tement opaques, celles avec 	de l'alpha ne
 sont plus antialias�e (conflit entre le code 	garantissant un alpha homog�ne
 et un raccordement ok). 	* (ZnRenderPolyline): Corrig� un bug dans le
 code garantissant 	un alpha homog�ne, qui conduit dans certains cas � une
 surcharge 	de couleur aux joints des segments de lignes (F.Decrock).

---
 generic/Draw.c | 59 +++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 46 insertions(+), 13 deletions(-)

(limited to 'generic/Draw.c')

diff --git a/generic/Draw.c b/generic/Draw.c
index 92b22b5..b408446 100644
--- a/generic/Draw.c
+++ b/generic/Draw.c
@@ -993,7 +993,7 @@ ZnRenderPolygonRelief(WidgetInfo	*wi,
 		      ZnBool		smooth,
 		      ZnPoint		*points,
 		      int		num_points,
-		      int		line_width)
+		      ZnReal		line_width)
 {
   PolygonData	pd;
 
@@ -1013,7 +1013,7 @@ void
 ZnRenderPolyline(WidgetInfo	*wi,
 		 ZnPoint	*points,
 		 int		num_points,
-		 int		line_width,
+		 ZnReal		line_width,
 		 LineStyle	line_style,
 		 int		cap_style,
 		 int		join_style,
@@ -1024,7 +1024,7 @@ ZnRenderPolyline(WidgetInfo	*wi,
   int		num_clips = ZnListSize(wi->clip_stack);
   ZnPoint	end_points[LINE_END_POINTS];
   ZnBool	need_rcaps, thin, closed;
-  int		pass, i, k, m;
+  int		pass, num_passes, i, k, m;
   ZnPoint	c1, c2;    
   XColor	*color;
   int		alpha;
@@ -1045,14 +1045,41 @@ ZnRenderPolyline(WidgetInfo	*wi,
   glColor4us(color->red, color->green, color->blue, alpha);
   ZnSetLineStyle(wi, line_style);
   glLineWidth(line_width);
-  glPointSize(line_width);
+  if (thin && (alpha != 65535)) {
+    /*
+     * This makes a special case for transparent lines.
+     * In this case we need to avoid drawing twice a
+     * single pixel. To achieve this we use the stencil
+     * buffer to protect already drawn pixels, unfortunately
+     * using antialiasing write in the stencil even if
+     * the pixel area is not fully covered resulting in
+     * a crack that can't be covered by points later on.
+     * To handle this case we need to disable the stencil
+     * which in turn result in erroneous alpha coverage.
+     *
+     * We have chosen to drawn transparent lines with a
+     * correct coverage but NOT antialiased.
+     */
+    glPointSize(line_width>1?line_width-1:line_width);
+    glDisable(GL_LINE_SMOOTH);
+  }
+  else {
+    glPointSize(line_width);
+  }
 
-  for (pass = 0; pass < 2; pass++) {
-    if (pass == 0) {
-      GLX_START_CLIP(num_clips, True);
-    }
-    else {
-      GLX_RESTORE_STENCIL(num_clips, False);
+  num_passes = 1;
+  if (alpha != 65535) {
+    num_passes = 2;
+  }
+    
+  for (pass = 0; pass < num_passes; pass++) {
+    if (alpha != 65535) {
+      if (pass == 0) {
+	GLX_START_CLIP(num_clips, True);
+      }
+      else {
+	GLX_RESTORE_STENCIL(num_clips, False);
+      }
     }
     if (first_end) {
       GetLineEnd(&points[0], &points[1], line_width, cap_style,
@@ -1092,13 +1119,13 @@ ZnRenderPolyline(WidgetInfo	*wi,
       glEnd();
     }
 
-    if (pass == 0) {
+    /* if (pass == 0) {
       GLX_RENDER_CLIPPED();
     }
     else {
       GLX_END_CLIP(num_clips);
-      return;
-    }
+      break;
+    }*/
     need_rcaps = ((line_width > 1) && (cap_style == CapRound));
     i = 0;
     k = num_points;
@@ -1111,6 +1138,7 @@ ZnRenderPolyline(WidgetInfo	*wi,
     if ((!need_rcaps && !closed) || last_end) {
       k--;
     }
+
     if (thin) {
       glBegin(GL_POINTS);
       for ( ; i < k; i++) {
@@ -1135,6 +1163,11 @@ ZnRenderPolyline(WidgetInfo	*wi,
       }
     }
   }
+  
+  GLX_END_CLIP(num_clips);
+  if (thin) {
+    glEnable(GL_LINE_SMOOTH);
+  }
 }
 
 
-- 
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