FreeLists / arachne / [arachne] Re: skewed BMPs.....

["Michal H. Tyc" <mht@xxxxxxxxxxxxxxxx>]

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Hi Glenn,

>> Michal,

>> After reading your message, I went to see if I could fix it also.

>> Did I come-up-with the same fix as you ?

>>  if(type==4)
>>  {
>>   k=bmp->size_x%8;
>> //!!glennmcc: May 07, 2004 -- Michal Tyc pointed out this error
>> // in rounding which causes some BMPs to be 'skewed' when displayed
>>   linebytes=(bmp->size_x+k)/2;
>> //  linebytes=bmp->size_x/2;
>>  }

Not exactly, although the 'mathematical' effect is identical (line
length is rounded up to the next multiply of 4 bytes). Here is my
code to replace a larger piece of HDRAWBMP.C, somewhat reformatted
for clarity:

{
  int l;                     // local to help making it register

  l = bmp->size_x;           // assume 8 bits per pixel (256 colors)
  if (type == 4)             // 4 bits per pixel (16 colors):
    l = (l + 1) >> 1;        //   convert nibbles to bytes
  else if (type == 24)       // 24 bits per pixel (truecolor):
    l *= 3;                  //   convert RGB triples to bytes
  else if (type != 8)        // unsupported (as bmpmono 1 bit per pixel)
    goto err;
  linebytes = (l + 3) & ~3;  // round up to next doubleword boundary
}


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