From 6d1a9dcc296fcaf6a275e7dd32e87fa81ffd26e9 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Tue, 8 Jan 2013 14:15:06 +0530
Subject: [PATCH] Fix clipping, considering that the clip path depends on the
 current painter transform, therefore the order of updateState() operations
 matters. So only track if the clip has been updated and always re-apply if it
 has.

---
 src/calibre/ebooks/pdf/render/graphics.py | 25 +++++++++++++----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/src/calibre/ebooks/pdf/render/graphics.py b/src/calibre/ebooks/pdf/render/graphics.py
index 71a8a22e85..7fb87662b4 100644
--- a/src/calibre/ebooks/pdf/render/graphics.py
+++ b/src/calibre/ebooks/pdf/render/graphics.py
@@ -11,7 +11,7 @@ from math import sqrt
 from collections import namedtuple
 
 from PyQt4.Qt import (
-    QBrush, QPen, Qt, QPointF, QTransform, QPainterPath, QPaintEngine, QImage)
+    QBrush, QPen, Qt, QPointF, QTransform, QPaintEngine, QImage)
 
 from calibre.ebooks.pdf.render.common import (
     Name, Array, fmtnum, Stream, Dictionary)
@@ -248,7 +248,7 @@ class TexturePattern(TilingPattern):
 class GraphicsState(object):
 
     FIELDS = ('fill', 'stroke', 'opacity', 'transform', 'brush_origin',
-                  'clip', 'do_fill', 'do_stroke')
+                  'clip_updated', 'do_fill', 'do_stroke')
 
     def __init__(self):
         self.fill = QBrush()
@@ -256,7 +256,7 @@ class GraphicsState(object):
         self.opacity = 1.0
         self.transform = QTransform()
         self.brush_origin = QPointF()
-        self.clip = QPainterPath()
+        self.clip_updated = False
         self.do_fill = False
         self.do_stroke = True
         self.qt_pattern_cache = {}
@@ -274,7 +274,7 @@ class GraphicsState(object):
         ans.opacity = self.opacity
         ans.transform = self.transform * QTransform()
         ans.brush_origin = QPointF(self.brush_origin)
-        ans.clip = self.clip
+        ans.clip_updated = self.clip_updated
         ans.do_fill, ans.do_stroke = self.do_fill, self.do_stroke
         return ans
 
@@ -311,7 +311,7 @@ class Graphics(object):
             s.opacity = state.opacity()
 
         if flags & QPaintEngine.DirtyClipPath or flags & QPaintEngine.DirtyClipRegion:
-            s.clip = painter.clipPath()
+            s.clip_updated = True
 
     def reset(self):
         self.current_state = GraphicsState()
@@ -326,7 +326,7 @@ class Graphics(object):
         ps = self.pending_state
         pdf = self.pdf
 
-        if (ps.transform != pdf_state.transform or ps.clip != pdf_state.clip):
+        if ps.transform != pdf_state.transform or ps.clip_updated:
             pdf.restore_stack()
             pdf.save_stack()
             pdf_state = self.base_state
@@ -341,11 +341,14 @@ class Graphics(object):
             pdf_state.brush_origin != ps.brush_origin):
             self.apply_fill(ps, pdf_system, painter)
 
-        if (pdf_state.clip != ps.clip):
-            p = convert_path(ps.clip)
-            fill_rule = {Qt.OddEvenFill:'evenodd',
-                        Qt.WindingFill:'winding'}[ps.clip.fillRule()]
-            pdf.add_clip(p, fill_rule=fill_rule)
+        if ps.clip_updated:
+            ps.clip_updated = False
+            path = painter.clipPath()
+            if not path.isEmpty():
+                p = convert_path(path)
+                fill_rule = {Qt.OddEvenFill:'evenodd',
+                            Qt.WindingFill:'winding'}[path.fillRule()]
+                pdf.add_clip(p, fill_rule=fill_rule)
 
         self.current_state = self.pending_state
         self.pending_state = None