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fast bresenham bitmap scaler in C

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simple and fast bresenham image scaler, no interpolation

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  1. // This code snippet demonstrates the simplest bresenham image scaling algorithm.
  2. // I use it for fast, non-interpolated image upsampling on an 16bit 20MHz MCU.
  3. // You will notice that all inner loops are quite easy on cpu - there are
  4. // only additions and a few cmp's.
  5. // Also, all memory addressing (in inner loops) is done indirectly, which is
  6. // in general much faster than recalculating absolute addresses.
  7. // Note that in my case pixels are not 24 bit RGB triplets, but 8bit 422 packed
  8. // format. You can easily extend this to 3 lookups and writes instead of 1 (for
  9. // genuine 24bit RGB).
  10. //
  11. // Hope it helps :)
  12. // written by akiko / agt, 2012
  13. // http://dev.modmancer.com
  14.  
  15. #define DEMO_WIDTH 64
  16. #define DEMO_HEIGHT 64
  17. #define FB_WIDTH 320
  18. #define FB_HEIGHT 240
  19.  
  20. unsigned int pixels_written = 0;
  21. UINT8 *src = framebuffer;	// input buffer of size DEMO_WIDTH * DEMO_HEIGHT
  22. UINT8 *dst = buffer;		// output buffer of size FB_WIDTH * FB_HEIGHT
  23.  
  24. int xint_part = DEMO_WIDTH / FB_WIDTH;
  25. int xfrac_part = DEMO_WIDTH % FB_WIDTH;
  26.  
  27. int yint_part = DEMO_HEIGHT / FB_HEIGHT;
  28. int yfrac_part = DEMO_HEIGHT % FB_HEIGHT;
  29. int ye = 0;
  30.  
  31. int dsty = 0;
  32. int xe = 0;
  33.  
  34. while (dsty < FB_HEIGHT)
  35. {
  36. 	int num_pixels = FB_WIDTH;
  37. 	while (num_pixels-- > 0)
  38. 	{
  39. 		*dst++ = *src;
  40. 		src += xint_part;
  41. 		xe += xfrac_part;
  42. 		if (xe >= FB_WIDTH)
  43. 		{
  44. 			xe -= FB_WIDTH;
  45. 			src++;
  46. 		}
  47. 	}
  48.  
  49. 	// use bresenham to increase line counter
  50. 	dsty += yint_part;
  51. 	ye += yfrac_part;
  52. 	if(ye >= FB_HEIGHT)
  53. 	{
  54. 		ye -= FB_HEIGHT;
  55. 		dsty++;
  56. 	}
  57. }

URL: bresenham scaling

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