PDF 着色类型 1（基于函数）和 FunctionType 4（PostScriptt 计算器函数）的简单示例

Question

I am trying to write custom function for PDF shading using Type 1 (Function based) shading with FunctionType 4 (Postscript calculator). Here's what I tried as a base:

...
5 0 obj
<<
/Type /Page
/Parent 1 0 R
/MediaBox [0 0 500 400]
/Resources << /Shading << /Sh1 8 0 R  >> >>
/Contents 6 0 R
>>
endobj
6 0 obj  %Contents
<<
/Length 37
>>
stream
2 J
0 200 200 200 re
q
W n        %clip to 200x200 rectangle
/Sh1 sh    %fill with shading
Q
endstream
endobj
7 0 obj  %The function itself
<<
/FunctionType 4
/Domain [0 1 0 1]
/Range [0 1 0 1 0 1]
/Length 24
>>
stream
{
pop  %pop parameters - I guess these are x, y coordinates (?)
pop
0.5   %half red , green, blue = gray
0.5
0.5
}
endstream
endobj
8 0 obj       %The shading
<<
/ShadingType 1
/ColorSpace /DeviceRGB
/Function 7 0 R
>>
endobj
...

I think this should make the square 200x200 gray. But the result is nothing - the canvas stays empty (tried in Adobe PDF reader).

Could anybody tell me what am I doing wrong?

Or - can someone provide an example of such kind of PDF - with custom shading function? I need something to start with. (Later I want to implement radial shading with repeating mode for my SWF to PDF converter using that function)

I haven't found any related PDF examples on the internet with Shading Type 1.

Answer 1

I found the problem now.

/FunctionType 4
/Domain [0 1 0 1]

I set the domain of function to 0-1, which will crop the coordinates to maximum of 1. For some reasons I though the incoming coordinates is 0-1.

Modification for

/FunctionType 4
/Domain [0 1000 0 1000]

works for me and the rectangle is gray.