pdf.js - A PDF with different outputs in different PDF viewers (with shades)

Question

Consider the following PostScript file

[1 0 0.5 0.866 150 550] concat
<< 
   /ShadingType 2 
   /Coords [ 0 0 100 100] 
   /BBox [ 0 0 100 100] 
   /ColorSpace [ /DeviceRGB ] 
   /Function 
      << 
         /FunctionType 0 
         /Domain [0 1] 
         /Range [0 1 0 1 0 1] 
         /BitsPerSample 8 
         /Size [2] 
         /DataSource <FFA0A0FFE0E0> 
      >>
   /Extend [false false] 
>> 
shfill

Consider that we convert that file in PDF with GhostScript (ps2pdf) or Adobe Distiller.

The resulting PDF does not render the same way in the different PDF viewers :

• In Adobe Reader or Firefox (which uses PDF.js), we have a parallelogram (not a rectangle).
• In SumatraPDF (which uses MuPDF) and Chrome (which uses PDFium), we have a rectangle.

Who is right?

question from:https://stackoverflow.com/questions/65907826/a-pdf-with-different-outputs-in-different-pdf-viewers-with-shades

Answer 1

In my opinion Adobe Acrobat is right but the specification could be read differently, too.

Your PDF contains the following content stream:

/GS1 gs
q
1 0 .5 .866 150 550 cm
/Sh1 sh
Q

I.e. first the current transformation matrix is changed, it is sheared and squished a bit, and then the shading Sh1 is painted. That shading in turn is defined as

<</BBox[0 0 100 100]/ColorSpace/DeviceRGB/Coords[0 0 100 100]/Function 15 0 R/ShadingType 2>>

I.e. with a 100×100 square bounding box (interpreted as a temporary additional clipping path) and an axial shading along its (0, 0) to (100, 100) diagonal, matching your postscript definition.

The shading operator sh is specified as

Operands	Operator	Description
name	sh	(PDF 1.3) Paint the shape and colour shading described by a shading dictionary, subject to the current clipping path. The current colour in the graphics state is neither used nor altered. The effect is different from that of painting a path using a shading pattern as the current colour. name is the name of a shading dictionary resource in the Shading subdictionary of the current resource dictionary (see 7.8.3, "Resource dictionaries"). All coordinates in the shading dictionary are interpreted relative to the current user space. (By contrast, when a shading dictionary is used in a Type 2 pattern, the coordinates are expressed in pattern space.) All colours are interpreted in the colour space identified by the shading dictionary’s ColorSpace entry (see "Table 77 — Entries common to all shading dictionaries"). The Background entry, if present, is ignored. This operator should be applied only to bounded or geometrically defined shadings. If applied to an unbounded shading, it paints the shading’s gradient fill across the entire clipping region, which may be time-consuming.