OpenGL顶点缓冲区不正确的渲染

Posted 2023-02-22

【中文标题】OpenGL顶点缓冲区不正确的渲染

【英文标题】：OpenGL Vertex Buffer incorrect render

【发布时间】：2013-10-27 05:30:10

【问题描述】：

我遇到了一个奇怪的问题。我正在尝试在我的 Windows 系统上使用 OpenGL 渲染一些数据。我在 opengl-tutorial.org 找到了一组针对 OpenGL 3.3 编写的教程。由于我的笔记本电脑（我在其中进行了大量开发）仅支持 OpenGL 2.1，因此我继续下载本教程的 OpenGL 2.1 端口。我对其进行了一些修改，添加了功能并对其进行了重构以实现可扩展性，但发现了一些奇怪的东西。每当我使用 Vertex Buffer Objects 渲染我的数据时，我得到的数据表示相当不正确。这如下所示。 http://www.majhost.com/gallery/DagonEcelstraun/Others/HelpNeeded/badrender.png 但是，当我使用 glVertex3fv 等指定我的数据时，我得到了更好的结果，如下所示。 http://www.majhost.com/gallery/DagonEcelstraun/Others/HelpNeeded/goodrender.png 这个问题出现在我的带有 Intel i3 集成显卡的 Windows 8.1 笔记本电脑和带有 nVidia GTX 660 的 Windows 7 台式机上，所以这不是硬件问题。有谁知道这里可能是什么问题？

加载网格数据：

const aiScene *scene = aiImportFile( sName.c_str(), 
aiProcessPreset_TargetRealtime_MaxQuality | aiProcess_FlipUVs );
const aiMesh *mesh = scene->mMeshes[0];
for( int i = 0; i < mesh->mNumVertices; i++ ) 
    meshData.push_back( mesh->mVertices[i][0] );
    meshData.push_back( mesh->mVertices[i][1] );
    meshData.push_back( mesh->mVertices[i][2] );

    meshData.push_back( mesh->mNormals[i][0] );
    meshData.push_back( mesh->mNormals[i][1] );
    meshData.push_back( mesh->mNormals[i][2] );

    meshData.push_back( mesh->mTextureCoords[0][i][0] );
    meshData.push_back( mesh->mTextureCoords[0][i][1] );
    meshData.push_back( 0 );

    meshData.push_back( mesh->mTangents[i][0] );
    meshData.push_back( mesh->mTangents[i][1] );
    meshData.push_back( mesh->mTangents[i][2] );


for( int i = 0; i < mesh->mNumFaces; i++ ) 
    for( int j = 0; j < 3; j++ ) 
        indices.push_back( mesh->mFaces[i].mIndices[j] );
    

第一次向显卡发送数据（在前面的代码之后调用）：

glGenBuffers( 1, &glVertData );
glBindBuffer( GL_ARRAY_BUFFER, glVertData );
glBufferData( GL_ARRAY_BUFFER, meshData.size() * sizeof( GLfloat ), &meshData[0], GL_STATIC_DRAW );

// Generate a buffer for the indices as well
glGenBuffers( 1, &glIndexes );
glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, glIndexes );
glBufferData( GL_ELEMENT_ARRAY_BUFFER, indices.size() * sizeof(unsigned short), &indices[0], GL_STATIC_DRAW );

渲染网格：

//Tell the shader to use our data
//bindVerts, bindUvs, bindNorms, and bindTangents refer to attribute variables in my shader
//vertexPosition_modelspace, vertexUV, vertexNormal_modelspace, and vertexTangent_modelspace, respectively.
this->verts = bindVerts;
this->uvs = bindUvs;
this->norms = bindNorms;
this->tangents = bindTangents;
glEnableVertexAttribArray( verts );
glEnableVertexAttribArray( uvs );
glEnableVertexAttribArray( norms );
glEnableVertexAttribArray( tangents );

//Specify how the graphics card should decode our data
// 1rst attribute buffer : vertices
glBindBuffer( GL_ARRAY_BUFFER, glVertData );
glVertexAttribPointer( verts, 3, GL_FLOAT, GL_FALSE, 12, (void*) 0 );

// 2nd attribute buffer : normals
glVertexAttribPointer( norms, 3, GL_FLOAT, GL_FALSE, 12, (void*) 3 ); 

//3rd attribute buffer : UVs
glVertexAttribPointer( uvs, 3, GL_FLOAT, GL_FALSE, 12, (void*) 6 );

//4th attribute buffer: tangents
glVertexAttribPointer( tangents, 3, GL_FLOAT, GL_FALSE, 12, (void*) 9 );

// Index buffer
glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, glIndexes );

//rendering the mesh with VBOs:
glDrawElements( GL_LINES, indices.size(), GL_UNSIGNED_SHORT, (void*) 0 );

//specifying the vertex data individually:
glBegin( GL_TRIANGLES );
int ind;
for( int i = 0; i < indices.size(); i++ ) 
    ind = indices[i] * 12;
    glNormal3fv( &meshData[ind + 3] );
    glTexCoord2fv( &meshData[ind + 6] );
    glVertex3fv( &meshData[ind] );

glEnd();

//clean up after the render
glDisableVertexAttribArray( verts );
glDisableVertexAttribArray( uvs );
glDisableVertexAttribArray( norms );
glDisableVertexAttribArray( tangents );

我的顶点着色器：

#version 130

// Input vertex data, different for all executions of this shader.
//it doesn't work, so we'll just get rid of it
attribute vec3 vertexPosition_modelspace;
attribute vec3 vertexUV;
attribute vec3 vertexNormal_modelspace;
attribute vec3 vertexTangent_modelspace;

// Output data ; will be interpolated for each fragment.
out vec2 UV;
out vec3 Position_worldspace;
out vec3 Normal_cameraspace;
out vec3 EyeDirection_cameraspace;
out vec3 LightDirection_cameraspace;
out vec4 ShadowCoord;

// Values that stay constant for the whole mesh.
uniform mat4 MVP;
uniform mat4 V;
uniform mat4 M;
uniform vec3 LightInvDirection_worldspace;
uniform mat4 DepthBiasMVP;
uniform sampler2D normalMap;

attribute vec3 vTangent;

void main() 
    // Output position of the vertex, in clip space : MVP * position
    gl_Position =  MVP * vec4( vertexPosition_modelspace, 1 );

    ShadowCoord = DepthBiasMVP *  vec4( vertexPosition_modelspace, 0 );

    // Position of the vertex, in worldspace : M * position
    Position_worldspace = ( M * vec4( vertexPosition_modelspace, 0 ) ).xyz;

    // Vector that goes from the vertex to the camera, in camera space.
    // In camera space, the camera is at the origin (0,0,0).
    EyeDirection_cameraspace = vec3( 0, 0, 0 ) - ( V * M *  vec4(         vertexPosition_modelspace, 0 ) ).xyz;

    // Vector that goes from the vertex to the light, in camera space
    LightDirection_cameraspace = ( V * vec4( LightInvDirection_worldspace, 0 ) ).xyz;

    // UV of the vertex. No special space for this one.
    UV = vertexUV.st;

    // Normal of the the vertex, in camera space
    // Only correct if ModelMatrix does not scale the model ! Use its inverse transpose if not.
    Normal_cameraspace = ( V * M * vec4( vertexNormal_modelspace.xyz, 0 ) ).xyz; 

片段着色器：

#version 130

// Interpolated values from the vertex shaders
in vec2 UV;
in vec3 Position_worldspace;
in vec3 Normal_cameraspace;
in vec3 EyeDirection_cameraspace;
in vec3 LightDirection_cameraspace;
in vec4 ShadowCoord;

out vec4 fragColor;

// Values that stay constant for the whole mesh.
uniform sampler2D diffuse;
uniform mat4 MV;
uniform vec3 LightPosition_worldspace;
uniform sampler2D shadowMap;
//uniform int shadowLevel;  //0 is no shadow, 1 is hard shadows, 2 is soft shadows, 3 is PCSS

// Returns a random number based on a vec3 and an int.
float random( vec3 seed, int i ) 
    vec4 seed4 = vec4( seed, i );           
    float dot_product = dot( seed4, vec4( 12.9898, 78.233, 45.164, 94.673 ) );
    return fract( sin( dot_product ) * 43758.5453 );


int mod( int a, int b ) 
    return a - (a / b);


void main() 
    int shadowLevel = 1;    //let's just do hard shadows
    // Light emission properties
    vec3 LightColor = vec3( 1, 1, 1 );
    float LightPower = 1.0f;

    // Material properties
    vec3 MaterialDiffuseColor = texture( diffuse, UV ).rgb;
    vec3 MaterialAmbientColor = vec3( 0.1, 0.1, 0.1 ) * MaterialDiffuseColor;
    vec3 MaterialSpecularColor = vec3( 0.3, 0.3, 0.3 );

    vec3 n = normalize( Normal_cameraspace );
    vec3 l = normalize( LightDirection_cameraspace );
    float cosTheta = clamp( dot( n, l ), 0.2, 1 );

    // Eye vector (towards the camera)
    vec3 E = normalize( EyeDirection_cameraspace );
    // Direction in which the triangle reflects the light
    vec3 R = reflect( -l, n );
    // Cosine of the angle between the Eye vector and the Reflect vector,
    // clamped to 0
    //  - Looking into the reflection -> 1
    //  - Looking elsewhere -> < 1
    float cosAlpha = clamp( dot( E, R ), 0, 1 );

    float visibility = 1.0;

    //variable bias
    float bias = 0.005 * tan( acos( cosTheta ) );
    bias = clamp( bias, 0, 0.01 );

    // dFragment to the light
    float dFragment = ( ShadowCoord.z-bias ) / ShadowCoord.w;
    float dBlocker = 0;
    float penumbra = 1;
    float wLight = 5.0;

    if( shadowLevel == 3 ) 
        // Sample the shadow map 8 times
        float count = 0;
        float temp;
        float centerBlocker = texture( shadowMap, ShadowCoord.xy).r;
        float scale = (wLight * (dFragment - centerBlocker)) / dFragment;
        for( int i = 0; i < 16; i++ )     
            temp = texture( shadowMap, ShadowCoord.xy + (scale * poissonDisk( i ) / 50.0) ).r;
            if( temp < dFragment ) 
                dBlocker += temp;
                count += 1;    
            
        

        if( count > 0 ) 
            dBlocker /= count;
            penumbra = wLight * (dFragment - dBlocker) / dFragment;
        
    

    if( shadowLevel == 1 ) 
        if( texture( shadowMap,  ShadowCoord.xy).r < dFragment ) 
            visibility -= 0.8;
        
     else if( shadowLevel > 1 ) 
        float iterations = 32;
        float sub = 0.8f / iterations;
        for( int i = 0; i < iterations; i++ ) 
            int index = mod( int( 32.0 * random( gl_FragCoord.xyy, i ) ), 32 );
            if( texture( shadowMap,  ShadowCoord.xy + (penumbra * poissonDisk( index ) / 250.0) ).r < dFragment ) 
                visibility -= sub;
            
        
    
    visibility = min( visibility, cosTheta );
    //MaterialDiffuseColor = vec3( 0.8, 0.8, 0.8 );
    fragColor.rgb = MaterialAmbientColor +
        visibility * MaterialDiffuseColor * LightColor * LightPower +
        visibility * MaterialSpecularColor * LightColor * LightPower * pow( cosAlpha, 5             );

请注意， poissonDisk( int ind ) 返回一个 vec2，其幅度不超过 1，属于泊松磁盘分布。尽管我使用的是着色器版本 130，但我使用的是函数而不是数组，因为数组在我的笔记本电脑上运行得相当慢。

在进行任何渲染之前，我会绑定该着色器。我还确保将正确的变量上传到我的所有制服，但我没有显示以节省空间，因为我知道它工作正常。

有谁知道是什么导致了这个不正确的渲染？

【参考方案1】：

首先，停止使用GL_LINES 绘制VBO。立即模式和 VBO 绘图使用相同的原始模式。

另外，从什么时候开始 3*4 = 3？当使用交错数据结构时，VBO 顶点指针中的地址（偏移量）应该是元素数量乘以数据类型的大小。 GL_FLOAT 是 4 个字节，如果您有一个 3 分量的顶点位置，这意味着您的 VBO 中下一个字段的偏移量是 3*4 = (void *)12，而不是 (void *)3。对于每个额外的顶点数组指针，这个过程必须继续，它们都使用了不正确的偏移量。

同样，VBO 的步幅应该是 12 * sizeof (GLfloat) = 48，而不是 12。

【讨论】：

我这样做了，并从 nvoglv32.dll 中得到了一些错误，一些快速的谷歌搜索显示为我的 nVidia 卡的 OpenGL 驱动程序。具体来说，它告诉我从位置 0x00000000 读取时遇到问题。当我调用 glDrawElements 时，一些快速调试发现问题出在 Mesh::draw() 中。我还发现我正在尝试将顶点位置、法线、切线和 UV 发送到位置 0。一旦我解决了这个问题，它就非常有效。谢谢！