cairo: Implement function shading using mesh gradients

Gfx draws function shadings by subdividing the shading until the
colors are the same or the maximum subdivision is reached then fills
each cell with the color of the mid point of the cell. The solid
colors can result in a pixelated appearance.

This patch implements a cairo specific version of the function shading
that uses mesh gradients to draw each cell. By setting the corner of
each patch to the shading color at that point, the mesh gradient will
interpolate the colors resulting in a smooth appearance.

Bug 88394

1 files changed, 4 insertions, 1 deletions

diff --git a/poppler/CairoOutputDev.h b/poppler/CairoOutputDev.h
index 33dde0c5..1c9a18ca 100644
--- a/poppler/CairoOutputDev.h
+++ b/poppler/CairoOutputDev.h
@@ -112,7 +112,7 @@ public:
 #if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 12, 0)
   virtual GBool useShadedFills(int type) { return type <= 7; }
 #else
-  virtual GBool useShadedFills(int type) { return type < 4; }
+  virtual GBool useShadedFills(int type) { return type > 1 && type < 4; }
 #endif
 
   // Does this device use FillColorStop()?
@@ -169,6 +169,9 @@ public:
 				  double *mat, double *bbox,
 				  int x0, int y0, int x1, int y1,
 				  double xStep, double yStep);
+#if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 12, 0)
+  virtual GBool functionShadedFill(GfxState *state, GfxFunctionShading *shading);
+#endif
   virtual GBool axialShadedFill(GfxState *state, GfxAxialShading *shading, double tMin, double tMax);
   virtual GBool axialShadedSupportExtend(GfxState *state, GfxAxialShading *shading);
   virtual GBool radialShadedFill(GfxState *state, GfxRadialShading *shading, double sMin, double sMax);