btriangle.cpp

这是我做的一个VC++小程序

	//当前颜色
	float fRed = clr1.red + fIncR;
	float fGreen = clr1.green + fIncG;
	float fBlue = clr1.blue + fIncB;
	float fAlpha = clr1.alpha + fIncA;

	//填充方向
	int nDirection = (x1 < x2) ? 1 : -1;

	//当前x坐标
	int x = x1 + nDirection;


	//当前 z 坐标, z坐标增量,
	//注意 我们并没有采用平面系数法计算深度
	float z = z1, fIncZ = (z2 - z1) / nFillPixels;
	z += fIncZ;

	nFillPixels--;
	//开始填充
	for(int i = 0; i < nFillPixels ; i++)
	{
		float zInBuffer = pZB->GetDepth(x,nScanLine);
				
		//如果当前点的z坐标小于深度缓冲区中的相同位置z的坐标
		if(z < zInBuffer)
		{
			//在颜色缓冲区中绘制第一个点
			pCB->SetPixel(x, nScanLine, fRed, fGreen, fBlue, fAlpha); 

			//重置深度缓冲区的值
			pZB->SetDepth(x, nScanLine, z);
		}

		//增量计算
		x += nDirection;
		z += fIncZ;
		fRed += fIncR;
		fGreen += fIncG;
		fBlue += fIncB;
		fAlpha += fIncA;
	}
} 

//扫描转换三角形
//pt1,pt2,pt3------三角形顶点坐标
//z1, z2,z3--------三角形顶点深度
//clr1,clr2,clr3---三角形顶点颜色
//pCB,pZB----------颜色缓冲器和深度缓冲器
void CBTriangle::Draw(POINT pt1, POINT pt2, POINT pt3, float z1, float z2, float z3, FLOATCOLORRGBA clr1, FLOATCOLORRGBA clr2, FLOATCOLORRGBA clr3, CColorBuffer* pCB, CZBuffer* pZB)
{
	ASSERT(pCB);
	ASSERT(pZB);
	
	//第一部分代码:处理退化情况中的一种情况

	//处理退化情况(三点在一条水平直线上)
	//尽管 z-buffer算法与绘制顺序一般情况下是无关的,
	//但是,当三点在一条扫描线上时,仍然有必要这样处理
	if((pt1.y == pt2.y) && (pt2.y == pt3.y))
	{
		//pt1位于中间(采用矢量点积进行判断)
		if((pt2.x - pt1.x) * (pt3.x - pt1.x) <= 0)
		{
			Scan(pt1.x, pt2.x, pt1.y, z1, z2, clr1, clr2, pCB, pZB);
			Scan(pt1.x, pt3.x, pt1.y, z1, z3, clr1, clr3, pCB, pZB);
		}
		//pt2位于中间
		else if((pt1.x - pt2.x) * (pt3.x - pt2.x) <= 0)
		{
			Scan(pt2.x, pt1.x, pt1.y, z2, z1, clr2, clr1, pCB, pZB);
			Scan(pt2.x, pt3.x, pt1.y, z2, z3, clr2, clr3, pCB, pZB);
		}
		//pt3位于中间
		else 
		{
			Scan(pt3.x, pt1.x, pt1.y, z3, z1, clr3, clr1, pCB, pZB);
			Scan(pt3.x, pt2.x, pt1.y, z3, z2, clr3, clr2, pCB, pZB);
		}

		//增加三个端点
		float zInBuffer = pZB->GetDepth(pt1.x, pt1.y);
				
		//如果当前点的z坐标小于深度缓冲区中的相同位置z的坐标
		if(z1 < zInBuffer)
		{
			//在颜色缓冲区中绘制第一个点
			pCB->SetPixel(pt1.x, pt1.y, clr1.red, clr1.green, clr1.blue, clr1.alpha);
			//重置深度缓冲区的值
			pZB->SetDepth(pt1.x, pt1.y, z1);
		}

		//
		zInBuffer = pZB->GetDepth(pt2.x, pt2.y);
				
		//如果当前点的z坐标小于深度缓冲区中的相同位置z的坐标
		if(z2 < zInBuffer)
		{
			//在颜色缓冲区中绘制第一个点
			pCB->SetPixel(pt2.x, pt2.y, clr2.red, clr2.green, clr2.blue, clr2.alpha);
			//重置深度缓冲区的值
			pZB->SetDepth(pt2.x, pt2.y, z2);
		}

		zInBuffer = pZB->GetDepth(pt3.x, pt3.y);
				
		//如果当前点的z坐标小于深度缓冲区中的相同位置z的坐标
		if(z3 < zInBuffer)
		{
			//在颜色缓冲区中绘制第一个点
			pCB->SetPixel(pt3.x, pt3.y, clr3.red, clr3.green, clr3.blue, clr3.alpha);
			//重置深度缓冲区的值
			pZB->SetDepth(pt3.x, pt3.y, z3);
		}

		return;
	}

	/////////////////////////////////////////////////////////////////////////////////////////////////
	
	//第二部分代码:处理一般情况

	//第一步,排序:
	//排序规则:第一个点的y坐标最小,第二个点的y坐标最大,第三个点则位于它们的中间
	//顶点和颜色备份

	POINT point1 = pt1, point2 = pt2, point3 = pt3;
	FLOATCOLORRGBA color1 = clr1, color2 = clr2, color3 = clr3;
	float fz1 = z1, fz2 = z2, fz3 = z3;

	//point1记录y坐标最小者
	if(point1.y > point2.y)
	{
		point1 = pt2;
		point2 = pt1;

		color1 = clr2;
		color2 = clr1;

		fz1 = z2;
		fz2 = z1;
	}
	if(point1.y > point3.y) 
	{
		POINT ptTemp = point1;
		FLOATCOLORRGBA clrTemp = color1;
		float zTemp = fz1;
		point1 = point3;
		color1 = color3;
		fz1 = fz3;

		point3 = ptTemp;
		color3 = clrTemp;
		fz3 = zTemp;
	}
	//point2记录y坐标最大者
	if(point2.y < point3.y)
	{
		POINT ptTemp = point2;
		FLOATCOLORRGBA clrTemp = color2;
		float zTemp = fz2;
		point2 = point3;
		color2 = color3;
		fz2 = fz3;

		point3 = ptTemp;
		color3 = clrTemp;
		fz3 = zTemp;
	}


	//第二步,获取边界点的 x 坐标,计算边界颜色
	//12 --- 1 to 2, 13 ---- 1 to 3,  32 ---- 3 to 2
	//y坐标之间的距离
	int nDy12 = (point2.y - point1.y) + 1;
	int nDy13 = (point3.y - point1.y) + 1;
	int nDy32 = (point2.y - point3.y) + 1;
	//获取扫描线的 x 坐标
	int* pnEdge12 = new int[nDy12];
	int* pnEdge13 = new int[nDy13];
	int* pnEdge32 = new int[nDy32];
		
	//获取边界颜色
	//注意,这里支持透明计算,因而颜色用三个分量
	FLOATCOLORRGBA* pClrEdge12 = new FLOATCOLORRGBA[nDy12];
	FLOATCOLORRGBA* pClrEdge13 = new FLOATCOLORRGBA[nDy13];
	FLOATCOLORRGBA* pClrEdge32 = new FLOATCOLORRGBA[nDy32];

	//记录边界深度
	float* pfzEdge12 = new float[nDy12];
	float* pfzEdge13 = new float[nDy13];
	float* pfzEdge32 = new float[nDy32];


	//获取边界及其颜色

	//计算矢量叉积(只需要计算Z分量),以判断三角形的位置关系
	int nDelta = ((point3.x - point1.x) * (point2.y - point3.y)
				 - (point2.x - point3.x) * (point3.y - point1.y));

	if(nDelta > 0)
	{
		DealEdge(point1.x, point1.y, point2.x, point2.y, fz1, fz2, color1, color2, pCB, pZB, pnEdge12, pClrEdge12, pfzEdge12); 
		DealEdge(point1.x, point1.y, point3.x, point3.y, fz1, fz3, color1, color3, pCB, pZB, pnEdge13, pClrEdge13, pfzEdge13, G3D_TRIANGLE_ON_LINE_LEFT); 
		DealEdge(point3.x, point3.y, point2.x, point2.y, fz3, fz2, color3, color2, pCB, pZB, pnEdge32, pClrEdge32, pfzEdge32, G3D_TRIANGLE_ON_LINE_LEFT); 
	}
	else
	{
		DealEdge(point1.x, point1.y, point2.x, point2.y, fz1, fz2, color1, color2, pCB, pZB, pnEdge12, pClrEdge12, pfzEdge12, G3D_TRIANGLE_ON_LINE_LEFT); 
		DealEdge(point1.x, point1.y, point3.x, point3.y, fz1, fz3, color1, color3, pCB, pZB, pnEdge13, pClrEdge13, pfzEdge13);
		DealEdge(point3.x, point3.y, point2.x, point2.y, fz3, fz2, color3, color2, pCB, pZB, pnEdge32, pClrEdge32, pfzEdge32);
	}

	//保证最后一个点也能绘制
	//这是因为,CPLine基元与Windows绘制直线的方式是一致的,即不绘制最后一个点

	float zInBuffer = pZB->GetDepth(point2.x, point2.y);
			
	//如果当前点的z坐标小于深度缓冲区中的相同位置z的坐标
	if(fz2 < zInBuffer)
	{
		//在颜色缓冲区中绘制第一个点
		pCB->SetPixel(point2.x, point2.y, color2.red, color2.green, color2.blue, color2.alpha);
		//重置深度缓冲区的值
		pZB->SetDepth(point2.x, point2.y, fz2);
	}
	//第三个顶点
	if(point3.y == point2.y)
	{
		zInBuffer = pZB->GetDepth(point3.x, point3.y);
				
		//如果当前点的z坐标小于深度缓冲区中的相同位置z的坐标
		if(fz3 < zInBuffer)
		{
			//在颜色缓冲区中绘制第一个点
			pCB->SetPixel(point3.x, point3.y, color3.red, color3.green, color3.blue, color3.alpha);
			//重置深度缓冲区的值
			pZB->SetDepth(point3.x, point3.y, fz3);
		}	
	}

	//第三步,进行扫描填充
	//扫描分为两个阶段:
	//第一,扫描第一点至第三点之间的区域
	//第二,扫描第三点至第二点之间的区域
	//当前扫描线的y坐标及扫描计数器
	int y, nPlumbScan = 0;
	if(point1.y < point3.y)
	{
		for(y = point1.y; y < point3.y; y++)
		{
			//一条扫描线的x坐标
			int	x12 = pnEdge12[nPlumbScan];
			int	x13 = pnEdge13[nPlumbScan];
			
			//一条扫描线的深度变化
			float z12 = pfzEdge12[nPlumbScan];
			float z13 = pfzEdge13[nPlumbScan];

			//颜色
			FLOATCOLORRGBA clrEdge12 = pClrEdge12[nPlumbScan];
			FLOATCOLORRGBA clrEdge13 = pClrEdge13[nPlumbScan];
			
			//填充
			Scan(x12, x13, y, z12, z13, clrEdge12,clrEdge13, pCB, pZB);

			nPlumbScan++;
		}//end for y
	
	}//end (point1.y < point3.y)
	
	//第二阶段扫描
	//准备数据
	//沿边3-2的计数器
	int nPlumbScan32 = 0;
	for(y = point3.y; y <= point2.y; y++)
	{
		//一条扫描线的x坐标
		int	x12 = pnEdge12[nPlumbScan];
		int	x32 = pnEdge32[nPlumbScan32];

		//一条扫描线的深度变化
		float z12 = pfzEdge12[nPlumbScan];
		float z32 = pfzEdge32[nPlumbScan32];

		//颜色
		FLOATCOLORRGBA clrEdge12 = pClrEdge12[nPlumbScan];
		FLOATCOLORRGBA clrEdge32 = pClrEdge32[nPlumbScan32];

		//填充
		Scan(x12, x32, y, z12, z32, clrEdge12,clrEdge32, pCB, pZB);

		nPlumbScan++;
		nPlumbScan32++;

	}//end for y

	delete[] pnEdge12;
	delete[] pnEdge13;
	delete[] pnEdge32;
	delete[] pClrEdge12;
	delete[] pClrEdge13;
	delete[] pClrEdge32;
	delete[] pfzEdge12;
	delete[] pfzEdge13;
	delete[] pfzEdge32;
}