D3D10与Geometry Shader学习笔记（2）

叁歲伎倆 2022-08-27 03:43 188阅读 0赞

[http://blog.csdn.net/javazjh/archive/2007/11/04/1866726.aspx][http_blog.csdn.net_javazjh_archive_2007_11_04_1866726.aspx]

华南理工大学，张嘉华 [newzjh@126.com][newzjh_126.com] QQ:188318005，欢迎和我多多交流，共同学习进步

**1.     贝赛尔曲线在Geometry Shader下的实现**

贝赛尔曲线在图形绘制中经常用到，在这一节里面讲介绍如何在Geometry Shader下实现贝赛尔曲线的绘制．首先来看最简单的贝赛尔曲线，就是由四个点控制．

考虑到贝赛尔曲线输入是四个点，而我们这里是为二维图形绘制实时的贝赛尔曲线，因此可以用两个四维的顶点表示这四个二维的点，因为对于Geometry Shader输入的类型中point必须是一个点，line是两个点，triangle是三个点，也就是input数组的大小，而不存在四个元素的输入数组类型．在GS\_Bezier()首先把两个四维的点转换为四个二维的点．接着根据贝赛尔曲线的函数，通过100次线段细分来逼近曲线，因此t=1/100，计算t1,t2为处于整段曲线的比例，接着利用贝赛尔曲线函数计算出每个线段的两端的两个点，接着Append到输出流，每输出一段线段都需要RestartStrip()一下，以确认以之前append的数据构成图元输出了．输出流这里定义为LineStream表示线段流．下面是HLSL文件，重点是Geometry Shader的代码：

struct GSIn

float4 pos          : POSITION;

\};

GSIn VS\_Bezier(int i : TEXCOORD0)

GSIn Output;

Output.pos = pos\[i\];

return Output;

\[maxvertexcount(100)\]

void GS\_Bezier(line GSIn input\[2\], inout LineStream<PS\_INPUT> LineOutputStream)

float2 positions\[4\];

positions\[0\]=input\[0\].pos.xy;

positions\[1\]=input\[0\].pos.zw;

positions\[2\]=input\[1\].pos.xy;

positions\[3\]=input\[1\].pos.zw;

for(int i=0;i<=99;i++)

float t1=i\*0.01;

float x1=positions\[0\].x\*(1-t1)\*(1-t1)\*(1-t1)+positions\[1\].x\*(1-t1)\*(1-t1)\*3\*t1+positions\[2\].x\*(1-t1)\*3\*t1\*t1+positions\[3\].x\*t1\*t1\*t1;

float y1=positions\[0\].y\*(1-t1)\*(1-t1)\*(1-t1)+positions\[1\].y\*(1-t1)\*(1-t1)\*3\*t1+positions\[2\].y\*(1-t1)\*3\*t1\*t1+positions\[3\].y\*t1\*t1\*t1;

float t2=(i+1)\*0.01;

float x2=positions\[0\].x\*(1-t2)\*(1-t2)\*(1-t2)+positions\[1\].x\*(1-t2)\*(1-t2)\*3\*t2+positions\[2\].x\*(1-t2)\*3\*t2\*t2+positions\[3\].x\*t2\*t2\*t2;

float y2=positions\[0\].y\*(1-t2)\*(1-t2)\*(1-t2)+positions\[1\].y\*(1-t2)\*(1-t2)\*3\*t2+positions\[2\].y\*(1-t2)\*3\*t2\*t2+positions\[3\].y\*t2\*t2\*t2;

PS\_INPUT output1;

output1.Pos=float4(x1,y1,0.0f,1.0f);

output1.color=float4(1,1,1,1);

output1.uv=float2(0,0);

LineOutputStream.Append(output1);

PS\_INPUT output2;

output2.Pos=float4(x2,y2,0.0f,1.0f);

output2.color=float4(1,1,1,1);

output2.uv=float2(0,0);

LineOutputStream.Append(output2);

LineOutputStream.RestartStrip();

float4 PS\_Bezier(PS\_INPUT input) : SV\_Target

return input.color;

technique10 Bezier

pass P0

SetVertexShader( CompileShader( vs\_4\_0, VS\_Bezier() ) );

SetGeometryShader( CompileShader( gs\_4\_0, GS\_Bezier() ) );

SetPixelShader( CompileShader( ps\_4\_0, PS\_Bezier() ) );

SetBlendState( AdditiveBlending, float4( 0.0f, 0.0f, 0.0f, 0.0f ), 0xFFFFFFFF );

SetDepthStencilState( DisableDepth, 0 );

下面是CPP文件，需要在其中调用IASetPrimitiveTopology( D3D10\_PRIMITIVE\_TOPOLOGY\_LINELIST )设置输入IA为线段列类型：

HRESULT G2DGraphics::DrawBezier(float x1,float y1,float x2,float y2,float x3,float y3,float x4,float y4,DWORD color)

HRESULT hr=S\_OK;

ID3D10Device\* pd3dDevice=GGraphicsDevice::GetDevice();

// 透明则略过

if (color>>24==0)

return S\_OK;

float fdevvicewidth=(float)(GGraphicsDevice::GetDeviceWidth());

float fdeviceheight=(float)(GGraphicsDevice::GetDeviceHeight());

float4 positions\[4\];

float4 colors\[4\];

float4 uvs\[4\];

positions\[0\].x=((float)(x1)/fdevvicewidth-0.5f)\*2.0f;

positions\[0\].y=((float)(y1)/fdeviceheight-0.5f)\*-2.0f;

positions\[0\].z=((float)(x2)/fdevvicewidth-0.5f)\*2.0f;

positions\[0\].w=((float)(y2)/fdeviceheight-0.5f)\*-2.0f;

colors\[0\]=ConvertColorFromDwordToFloat4(color);

positions\[1\].x=((float)(x3)/fdevvicewidth-0.5f)\*2.0f;

positions\[1\].y=((float)(y3)/fdeviceheight-0.5f)\*-2.0f;

positions\[1\].z=((float)(x4)/fdevvicewidth-0.5f)\*2.0f;

positions\[1\].w=((float)(x4)/fdevvicewidth-0.5f)\*2.0f;

colors\[1\]=ConvertColorFromDwordToFloat4(color);

g\_VertexPositions->SetFloatVectorArray((float\*)&positions,0,4);

g\_VertexColors->SetFloatVectorArray((float\*)&colors,0,4);

// Set the input layout

pd3dDevice->IASetInputLayout( g\_pVertexLayout );

// Set vertex buffer

UINT stride = sizeof( UINT );

UINT offset = 0;

pd3dDevice->IASetVertexBuffers( 0, 1, &g\_pVertexBuffer, &stride, &offset );

pd3dDevice->IASetPrimitiveTopology( D3D10\_PRIMITIVE\_TOPOLOGY\_LINELIST );

D3D10\_TECHNIQUE\_DESC techDesc;

g\_pBezierTech->GetDesc( &techDesc );

for ( UINT p = 0; p < techDesc.Passes; ++p )

g\_pBezierTech->GetPassByIndex( p )->Apply(0);

pd3dDevice->Draw( 2, 0 );

return S\_OK;

**2. 圆形在Geometry Shader下的实现**

圆形在图形绘制中也经常用到，由半径和中心坐标控制，下面是实现的HLSL代码，同样也是通过把圆形细分为特定数量线段进行逼近，根据角度计算圆形上线段的两端顶点．

\[maxvertexcount(100)\]

void GS\_Circle(point GSIn input\[1\], inout LineStream<PS\_INPUT> LineOutputStream)

int number=40;

float2 position=input\[0\].pos.xy;

float radius=input\[0\].pos.z;

float dangle=3.1415926f\*2.0f/number;

for(int i=0;i<number;i++)

float t1=i\*dangle;

float x1=radius\*cos(t1)+position.x;

float y1=radius\*sin(t1)+position.y;

float t2=(i+1)\*dangle;

float x2=radius\*cos(t2)+position.x;

float y2=radius\*sin(t2)+position.y;

PS\_INPUT output1;

output1.Pos=float4(x1,y1,0.0f,1.0f);

output1.color=float4(1,1,1,1);

output1.uv=float2(0,0);

LineOutputStream.Append(output1);

PS\_INPUT output2;

output2.Pos=float4(x2,y2,0.0f,1.0f);

output2.color=float4(1,1,1,1);

output2.uv=float2(0,0);

LineOutputStream.Append(output2);

LineOutputStream.RestartStrip();

下面是CPP文件，输入类型为D3D10\_PRIMITIVE\_TOPOLOGY\_POINTLIST，因为只需要圆心坐标（ x,y）和半径，用一个四维顶点就可以存储了．

HRESULT G2DGraphics::DrawCircle(float x,float y,float r,DWORD color)

HRESULT hr=S\_OK;

ID3D10Device\* pd3dDevice=GGraphicsDevice::GetDevice();

// 透明则略过

if (color>>24==0)

return S\_OK;

float fdevvicewidth=(float)(GGraphicsDevice::GetDeviceWidth());

float fdeviceheight=(float)(GGraphicsDevice::GetDeviceHeight());

float4 positions\[4\];

float4 colors\[4\];

float4 uvs\[4\];

positions\[0\].x=((float)(x)/fdevvicewidth-0.5f)\*2.0f;

positions\[0\].y=((float)(y)/fdeviceheight-0.5f)\*-2.0f;

positions\[0\].z=((float)(r)/fdevvicewidth)\*2.0f;

colors\[0\]=ConvertColorFromDwordToFloat4(color);

g\_VertexPositions->SetFloatVectorArray((float\*)&positions,0,4);

g\_VertexColors->SetFloatVectorArray((float\*)&colors,0,4);

// Set the input layout

pd3dDevice->IASetInputLayout( g\_pVertexLayout );

// Set vertex buffer

UINT stride = sizeof( UINT );

UINT offset = 0;

pd3dDevice->IASetVertexBuffers( 0, 1, &g\_pVertexBuffer, &stride, &offset );

pd3dDevice->IASetPrimitiveTopology( D3D10\_PRIMITIVE\_TOPOLOGY\_POINTLIST );

D3D10\_TECHNIQUE\_DESC techDesc;

g\_pCircleTech->GetDesc( &techDesc );

for( UINT p = 0; p < techDesc.Passes; ++p )

g\_pCircleTech->GetPassByIndex( p )->Apply(0);

pd3dDevice->Draw( 1, 0 );

return S\_OK;

介绍了两种简单的二维图形在Geometry Shader的绘制后，在学习笔记3里将介绍较为复杂的Geometry Shader下的LOD应用．

[http_blog.csdn.net_javazjh_archive_2007_11_04_1866726.aspx]: http://blog.csdn.net/javazjh/archive/2007/11/04/1866726.aspx
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