How to draw a pixel line on a sprite represented by an array of color?

Question

I'm making my own graphics library and I have a Sprite class which is just an array of colors with a width and a height. I can set a pixel on the sprite by changing its color value. How can I draw a line on a sprite given a start position and an end position?

class Sprite
{
public:
    Sprite();

public:
    LongUtils::Pixel GetPixel(int32_t x, int32_t y) const;
    bool  SetPixel(int32_t x, int32_t y, Pixel p);
    LongUtils::Pixel* GetData(); // return the *data
    LongUtils::Pixel* GetBlockData(uint32_t x, uint32_t y, uint32_t w, uint32_t h);

private:
    LongUtils::Pixel* data = nullptr;
    int32_t width = 0;
    int32_t height = 0;
};

Answer 1

Use something like Bresenham's line algorithm. Here's an example:

void Line( float x1, float y1, float x2, float y2, const Color& color )
{
        // Bresenham's line algorithm
  const bool steep = (fabs(y2 - y1) > fabs(x2 - x1));
  if(steep)
  {
    std::swap(x1, y1);
    std::swap(x2, y2);
  }
 
  if(x1 > x2)
  {
    std::swap(x1, x2);
    std::swap(y1, y2);
  }
 
  const float dx = x2 - x1;
  const float dy = fabs(y2 - y1);
 
  float error = dx / 2.0f;
  const int ystep = (y1 < y2) ? 1 : -1;
  int y = (int)y1;
 
  const int maxX = (int)x2;
 
  for(int x=(int)x1; x<=maxX; x++)
  {
    if(steep)
    {
        SetPixel(y,x, color);
    }
    else
    {
        SetPixel(x,y, color);
    }
 
    error -= dy;
    if(error < 0)
    {
        y += ystep;
        error += dx;
    }
  }
}