Here is a simple program that works with floats, but replace float by double everywhere, including in the OpenCL code, and you get this:
Qt Code: 
  1. indata:
  2.   0,000000 1,000000 2,000000 3,000000 
  3.   1,000000 2,000000 3,000000 4,000000 
  4.   2,000000 3,000000 4,000000 5,000000 
  5.   3,000000 4,000000 5,000000 6,000000
  6. outdata:
  7.   0,000000 1,000000 2,000000 3,000000 
  8.   1,000000 2,000000 3,000000 4,000000 
  9.   0,000000 0,000000 0,000000 0,000000 
  10.   0,000000 0,000000 0,000000 0,000000
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So does it mean that QtOpenCL does not support doubles? It seems that it is not possible to setArg a double.
Qt Code: 
  1. QCLContext CLcontext;
  2. if (!CLcontext.create()) {
  3.   this->Warning("Could not create OpenCL context for the GPU\n");
  4.   qApp->quit();
  5. }
  6. QCLVector<double> inbuffer = CLcontext.createVector<double>(kernel_size.width()*kernel_size.height(), QCLMemoryObject::ReadOnly);
  7. QCLVector<double> outbuffer = CLcontext.createVector<double>(kernel_size.width()*kernel_size.height(), QCLMemoryObject::WriteOnly);
  8. int idx=0;
  9. for (int i=0 ; i<kernel_size.width() ; i++)
  10.   for (int j=0 ; j<kernel_size.height() ; j++,idx++)
  11.     inbuffer[idx] = (double)(i + j);
  12.  
  13. QCLProgram CLprogram = CLcontext.buildProgramFromSourceFile("./program.cl");
  14. QCLKernel CLkernel = CLprogram.createKernel("program");
  15. CLkernel.setGlobalWorkSize(kernel_size.width()*kernel_size.height());
  16. CLkernel.setArg(0, outbuffer);
  17. CLkernel.setArg(1, inbuffer);
  18.  
  19. CLkernel.run();
  20.  
  21. int id=0;
  22. this->Print("indata:");
  23. for (int j=0 ; j<kernel_size.height() ; j++) {
  24.   for (int i=0 ; i<kernel_size.width() ; i++,id++)
  25.     this->Print(" %lf\r", inbuffer[id]);
  26.   this->Print(" ");
  27. }
  28. id=0;
  29. this->Print("outdata:");
  30. for (int j=0 ; j<kernel_size.height() ; j++) {
  31.   for (int i=0 ; i<kernel_size.width() ; i++,id++)
  32.     this->Print(" %lf\r", outbuffer[id]);
  33.   this->Print(" ");
  34. }
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Qt Code: 
  1. __kernel void program(__global __write_only double *output,
  2. 		      __global __read_only double *input)
  3. {
  4.   unsigned int index = get_global_id(0);
  5.   output[index] = input[index];
  6. }
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