Creating a linear gradient in 2D array

Question

I have a 2D bitmap-like array of let\'s say 500*500 values. I\'m trying to create a linear gradient on the array, so the resulting bitmap would look something like this (in gray

Answer 1

I'll just post my solution.

int ColourAt( int x, int y )
{
  float imageX = (float)x / (float)BUFFER_WIDTH;
  float imageY = (float)y / (float)BUFFER_WIDTH;

  float xS = xStart / (float)BUFFER_WIDTH;
  float yS = yStart / (float)BUFFER_WIDTH;
  float xE = xEnd / (float)BUFFER_WIDTH;
  float yE = yEnd / (float)BUFFER_WIDTH;
  float xD = xE - xS;
  float yD = yE - yS;

  float mod = 1.0f / ( xD * xD + yD * yD );

  float gradPos = ( ( imageX - xS ) * xD + ( imageY - yS ) * yD ) * mod;

  float mag = gradPos > 0 ? gradPos < 1.0f ? gradPos : 1.0f : 0.0f;

  int colour = (int)( 255 * mag );
  colour |= ( colour << 16 ) + ( colour << 8 );
  return colour;
}

For speed ups, cache the derived "direction" values (hint: premultiply by the mag).