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 找到了一组为OpenGL 3.3编写的教程。由于我的笔记本电脑（我在那里做了大量的开发）只支持OpenGL 2.1，我继续下载本教程的OpenGL 2.1端口。我弄乱了它，添加功能并重构它以实现可扩展性，但注意到一些奇怪的东西。每当我使用顶点缓冲区对象渲染数据时，我都会得到一个相当不正确的数据表示形式。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，再次如下所示。http://www.majhost.com/gallery/DagonEcelstraun/Others/HelpNeeded/goodrender.png该问题既发生在带有Intel i3集成显卡的Windows 8.1笔记本电脑上，也发生在带有nVidia GTX 660的Windows 7台式机上，因此这不是硬件问题。有谁知道这里可能有什么问题？
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] );
}
}
首次将数据发送到显卡（在前面的代码之后立即调用）：
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，泊松磁盘（ int ind ） 返回一个大小不超过 1 的 vec2，它位于泊松盘分布中。即使我使用的是着色器版本 130，我也使用了函数而不是数组，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所有的制服上，但我没有展示以节省空间，因为我知道它工作正常。
有谁知道是什么导致了这种不正确的渲染？
好吧，首先，停止使用 GL_LINES 绘制 VBO。对即时模式和 VBO 绘图使用相同的基元模式。
另外，从什么时候开始 3*4 = 3？使用交错数据结构时，VBO 顶点指针中的地址（偏移量）应为元素数乘以数据类型的大小。 GL_FLOAT是 4 个字节，如果您有 3 分量顶点位置，这意味着 VBO 中下一个字段的偏移量为 3*4 = (void *)12 ，而不是 (void *)3 。对于每个额外的顶点数组指针，此过程必须继续，它们都使用不正确的偏移量。
同样，VBO 的步幅应该是 12 * sizeof （GLfloat） = 48，而不是 12。