// 主渲染函数
void DrawTrap(HTrapezoid trap)
{
//HScanline scanline;
int j, top, bottom;
top = (int)(trap.top + 0.5f);
bottom = (int)(trap.bottom + 0.5f);
for (j = top; j < bottom; j++)
{
if (j >= 0 && j < HScreenDevice.GetInstance().ScreenHeight) //todo
//插值得到梯形的腰的两个点
{
trap.EdgeInterp((float)j + 0.5f);
//初始化扫描线
HScanline scanline = GetScanline(trap, j);
//绘制扫描线
DrawScanline(scanline);
}
}
}
// 根据左右两边的端点，初始化计算出扫描线的起点和步长
HScanline GetScanline(HTrapezoid trap, int y)
{
HScanline scanlineRet = new HScanline();
// 左右两点的 宽度
float width = trap.right.v.pos.x - trap.left.v.pos.x;
// 起点X 坐标
scanlineRet.x = (int)(trap.left.v.pos.x + 0.5f);
// 宽度
scanlineRet.width = (int)(trap.right.v.pos.x + 0.5f) - scanlineRet.x;
// y坐标
scanlineRet.y = y;
// 扫描起点
scanlineRet.v = trap.left.v.Copy();
//
if (trap.left.v.pos.x >= trap.right.v.pos.x)
{
scanlineRet.width = 0;
}
//计算步伐
scanlineRet.step = trap.left.v.Step(trap.right.v, width);
return(scanlineRet);
}