RenderContext.java

public class RenderContext extends Bitmap{

	private final int m_scanBuffer[];

	public RenderContext(int width, int height){
		super(width,height);
		m_scanBuffer = new int[height * 2];
	}
	
	public void DrawScanBuffer(int yCoord, int xMin, int xMax){
		m_scanBuffer[yCoord * 2   ] = xMin;
		m_scanBuffer[yCoord * 2 +1] = xMax;
	}
	
	public void FillShape(int yMin, int yMax){
		
		for(int j = Math.max(0,yMin); j < Math.min(m_height,yMax); j++){
			int xMin = m_scanBuffer[j * 2];
			int xMax = m_scanBuffer[j * 2 + 1];
			for(int i = Math.max(0,xMin); i < Math.min(m_width,xMax); i++){
				DrawPixel(i,j, (byte)0xFF, (byte)0xFF, (byte)0xFF, (byte)0xFF);
			}
		}
	}

	public void FillTriangle(Vertex v1, Vertex v2, Vertex v3){
		Matrix4f screenSpaceTransform = new Matrix4f().InitScreenSpaceTransform(
			GetWidth()/2, GetHeight()/2);
		
		Vertex minYVert = v1.Transform(screenSpaceTransform).PerspectiveDivide();
		Vertex midYVert = v2.Transform(screenSpaceTransform).PerspectiveDivide();
		Vertex maxYVert = v3.Transform(screenSpaceTransform).PerspectiveDivide();
		
		if(maxYVert.GetY() < midYVert.GetY()){
			Vertex temp = maxYVert;
			maxYVert = midYVert;
			midYVert = temp;
		}
		
		if(midYVert.GetY() < minYVert.GetY()){
			Vertex temp = midYVert;
			midYVert = minYVert;
			minYVert = temp;
		}
		
		if(maxYVert.GetY() < midYVert.GetY()){
			Vertex temp = maxYVert;
			maxYVert = midYVert;
			midYVert = temp;
		}
		
		float area = minYVert.TriangleAreaTimesTwo(maxYVert , midYVert);
		int handedness = area >=0 ? 1 : 0;
		
		ScanConvertTriangle(minYVert, midYVert, maxYVert, handedness);
		
		
		FillShape((int)minYVert.GetY(),(int)maxYVert.GetY());
	}
	
	public void ScanConvertTriangle(Vertex minYVert, Vertex midYVert, 
			Vertex maxYVert, int handedness){
		ScanConvertLine(minYVert, maxYVert, 0 + handedness);
		ScanConvertLine(minYVert, midYVert, 1 - handedness);
		ScanConvertLine(midYVert, maxYVert, 1 - handedness);
	}
	
	private void ScanConvertLine(Vertex minYVert, Vertex maxYVert, int whichSide){
		int yStart = (int)minYVert.GetY();
		int yEnd   = (int)maxYVert.GetY();
		int xStart = (int)minYVert.GetX();
		int xEnd   = (int)maxYVert.GetX();
		
		int yDist = yEnd - yStart;
		int xDist = xEnd - xStart;
		
		if(yDist <= 0)
			return;
		
		float xStep = ((float)xDist)/((float)yDist);
		float curX = (float)Math.max(0,xStart);
		for(int j = Math.max(0,yStart); j < Math.min(yEnd,m_height); j++){
			m_scanBuffer[j * 2 + whichSide] = (int)curX;
			curX += xStep;
			if(curX>=m_width){
				break;
			}
		}
	}

}