faq Bitmap Encoding

[FHannes]

In SCAR Divi 3.31 I've made a small change to the encoding for bitmaps so it can very easily be encoded or decoded outside of SCAR.

 

The 'c' type bitmap encoding is set up by converting every pixel of the bitmap row-by-row into a RGB values and suing those in the same sequence as ANSI encoded characters to build a string formatted as 'RGBRGBRGB...', after this the string is compressed with the ZLib compression library and encoded in Base64. Finally 'c' is appended to the front of the string to indicate the encoding type.

 

Here an example of how a bitmap is manually decoded in SCAR (you need SCAR Divi 3.31):

[scar]var

Bmp, Bmp2, W, H, I, Color: Integer;

Str, Tmp: AnsiString;

 

begin

try

// Load bitmap

Bmp := BitmapFromString(19, 16, 'ceNplkwmWojAURd1Tb6HW0lvotfQW3EKBIKgoEAI' +

'IKFOCyiDI4A7sH1JSnOp33mH8l4Sfl/WxWDPnsptLznWyDHZv8Fw5lhu/2p3uWvjQ4w6lg' +

'0XBT3j1ZZexsnMDLxYL2b3CE+WYq165DUrtVB+ixkg6iwx29gTzSrA0ejHq9ZufR5yxxS6' +

'o9iGArUV7Oxvcy7DC2WSOzA2S7GztXDderp0rI24w6W06ONkgmKlgEgFRARE+ivnrmwKJK' +

'JUsojiXrV/oUW0lrU06h/afRjI65WXv8nHCrxccBT0UUSzbZHO8HU6lGdeYAPvgIB8IPLF' +

'wPX1ENELZYjVaUBhhjZIGpw1MlRdzc/b/OfOj5ud6dEdJDaBosZ78eWvCp/p5o0AGB5OGr' +

'9rHW3N8AudrZEQ1gt6mD8Ut4Ha5XH7MxPHvLgH+d/TI4pQ1R/Eq1at4wRzn4A+EC9PWoR0' +

'HVb/a+Pc5zsHpZ7/albSYJaeHdWQJ9wrFKxW/BFx94z+0jx6QNzPtMYWsDjbtV/gi2Syls' +

'BdYyFngYbOUkG01qLZBvT3Xu3Ozj9tD0plsazwxmAyfEDnEIieiDJaGhda+rJzb2snZTMZ' +

'fABD21CFu9bRH9GllgPf/ABzKAUs=');

// Convert the bitmap back to a string ^^^

Str := BitmapToString(Bmp);

// Get the dimensions of the bitmap

GetBitmapSize(Bmp, W, H);

finally

// Free the original bitmap

FreeBitmap(Bmp);

end;

 

// Create a new bitmap with the dimensions of the original

Bmp2 := BitmapFromString(W, H, '');

try

// Check the bitmap prefix (This is an indicator for the bitmap string format)

if Str[1] = 'c' then

begin

// Decode and decompress the bitmap with the prefix removed

Str := ZLibDecompress(Base64ToStr(Copy(Str, 2, Length(Str) - 1)));

// Loop through all pixels which are stored in the string as RGBRGBRGB...

for I := 0 to Length(Str) div 3 - 1 do

begin

// Get the RGB characters for the current pixel

Tmp := Copy(Str, I * 3 + 1, 3);

// Convert the RGB characters to a color

Color := RGBToColor(Byte(Tmp[1]), Byte(Tmp[2]), Byte(Tmp[3]));

// Calculate the coordinates of the color on the bitmap and color the pixel

FastSetPixel(Bmp2, I mod W, I div W, Color);

end;

// Show the new bitmap

DebugBitmap(Bmp2);

end;

finally

// Free the new bitmap

FreeBitmap(Bmp2);

end;

end.[/scar]

 

This insight should make it easier for people to for example encode bitmaps in PHP or other languages which can then be used in SCAR.

Edited February 10, 2012 by Freddy