bool FrontEndCullingByArea(VSOutput v0, VSOutput v1, VSOutput v2)
{
if (context.frontEndCull == FrontEndCull.Off)
{
return(true);
}
if (context.cullMode == CullMode.None)
{
return(true);
}
//cull back
Vector2 p0 = new Vector2(v0.position.X, v0.position.Y);
Vector2 p1 = new Vector2(v1.position.X, v1.position.Y);
Vector2 p2 = new Vector2(v2.position.X, v2.position.Y);
//做了透射除法,Culling准确点
p0 *= 1 / v0.position.W;
p1 *= 1 / v1.position.W;
p2 *= 1 / v2.position.W;
float area = Rasterizer.EdgeFunction(p0, p1, p2);
//在Clip Space, area >= 0表示顺时针
if (context.winding == Winding.Clockwise)
{
return(area > 0);
}
return(area < 0);
}
//裁剪前
public void DrawTriangle(VSOutput vClip0, VSOutput vClip1, VSOutput vClip2)
{
//Backface Culling
if (!FrontEndCulling(vClip0, vClip1, vClip2))
{
return;
}
context.statics.triangleCount += 1;
//Clipping
List <VSOutput> inputs = new List <VSOutput> {
vClip0, vClip1, vClip2
};
List <VSOutput> outputs = Clipping.Clip(inputs, context);
//输出结果是trianglefan
if (outputs.Count < 3)
{
//全裁剪掉了
return;
}
//画Triangle Fan
VSOutput v0 = outputs[0];
VSOutput vNDC0 = Rasterizer.PerspectiveDivide(v0);
if (vNDC0 == null)
{
return;
}
VSOutput vScreen0 = rasterizer.ViewportTransform(vNDC0);
for (int i = 1; i + 1 < outputs.Count; i += 1)
{
VSOutput v1 = outputs[i];
VSOutput v2 = outputs[i + 1];
VSOutput vNDC1 = Rasterizer.PerspectiveDivide(v1);
VSOutput vNDC2 = Rasterizer.PerspectiveDivide(v2);
if (vNDC1 == null || vNDC2 == null)
{
continue;
}
VSOutput vScreen1 = rasterizer.ViewportTransform(vNDC1);
VSOutput vScreen2 = rasterizer.ViewportTransform(vNDC2);
//检查Backface
if (i == 1)
{
//由于裁剪前后的三角形都在同一个平面上，所以只要检查第一个就够了
if (!BackfaceCulling(vScreen0, vScreen1, vScreen2))
{
return;
}
}
context.statics.rasterTriCount += 1;
rasterizer.RasterizeTriangle(vScreen0, vScreen1, vScreen2);
}
}
//初始化
void Init(Graphics g)
{
InitByGraphics(g);
//初始化Frame Buffer
RectangleF rect = graphics.VisibleClipBounds;
Size frameSize = new Size((int)rect.Width, (int)rect.Height);
context = new Context(frameSize);
rasterizer = new Rasterizer(context);
camera = new Camera();
}
public void Test_BarycentricRasterizeTriangle()
{
context.clearColor = Color.White;
Clear();
//假设n = 1, far = 2
//测试光栅化和插值
//第一个三角形,v0红色在中上，v1绿和v2蓝在中间的左右，v0在far plane， v1,v2在near plane
VSOutput v0 = new VSOutput();
v0.position = new Vector4(0f, 1f, 1f, 2f);
v0.color = new Vector4(1f, 0f, 0f, 1f);
VSOutput v1 = new VSOutput();
v1.position = new Vector4(-0.5f, -0.5f, -1f, 1f);
v1.color = new Vector4(0f, 1f, 0f, 1f);
VSOutput v2 = new VSOutput();
v2.position = new Vector4(0.5f, -0.5f, -1f, 1f);
v2.color = new Vector4(0f, 0f, 1f, 1f);
v0 = Rasterizer.PerspectiveDivide(v0);
v0 = rasterizer.ViewportTransform(v0);
v1 = Rasterizer.PerspectiveDivide(v1);
v1 = rasterizer.ViewportTransform(v1);
v2 = Rasterizer.PerspectiveDivide(v2);
v2 = rasterizer.ViewportTransform(v2);
rasterizer.BarycentricRasterizeTriangle(v0, v1, v2);
//测试depth test
//第二个三角形，v0红在近平面，v1,v2在远
v0.position = new Vector4(-0.5f, 0.5f, -1f, 1f);
v1.position = new Vector4(-2f, -1f, 1f, 2f);
v2.position = new Vector4(0f, -2f, 1f, 2f);
v0 = Rasterizer.PerspectiveDivide(v0);
v0 = rasterizer.ViewportTransform(v0);
v1 = Rasterizer.PerspectiveDivide(v1);
v1 = rasterizer.ViewportTransform(v1);
v2 = Rasterizer.PerspectiveDivide(v2);
v2 = rasterizer.ViewportTransform(v2);
rasterizer.BarycentricRasterizeTriangle(v0, v1, v2);
//第三个三角形，v1绿在近，其他在远平面
v0.position = new Vector4(-2f, 0f, 1f, 2f);
v1.position = new Vector4(-0.5f, -1f, -1f, 1f);
v2.position = new Vector4(0f, -1f, 1f, 2f);
v0 = Rasterizer.PerspectiveDivide(v0);
v0 = rasterizer.ViewportTransform(v0);
v1 = Rasterizer.PerspectiveDivide(v1);
v1 = rasterizer.ViewportTransform(v1);
v2 = Rasterizer.PerspectiveDivide(v2);
v2 = rasterizer.ViewportTransform(v2);
rasterizer.BarycentricRasterizeTriangle(v0, v1, v2);
}
bool BackfaceCulling(VSOutput vScreen0, VSOutput vScreen1, VSOutput vScreen2)
{
if (context.cullMode == CullMode.None)
{
return(true);
}
if (context.frontEndCull == FrontEndCull.On)
{
return(true);
}
Vector2 p0 = new Vector2(vScreen0.posScreen.X, vScreen0.posScreen.Y);
Vector2 p1 = new Vector2(vScreen1.posScreen.X, vScreen1.posScreen.Y);
Vector2 p2 = new Vector2(vScreen2.posScreen.X, vScreen2.posScreen.Y);
float area = Rasterizer.EdgeFunction(p0, p1, p2);
if (context.winding == Winding.Clockwise)
{
return(area < 0);
}
//在Viewport Space, 由于Y轴向下, area > 0表示逆时针
return(area > 0);
}
