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In my OpenGL program I have two shaders. One renders with textures, and the other renders just solid colors. After compiling and linking a shader, I enable a texture coordinate vertex attribute array depending on weather or not the shader contains the attribute.

//This code is called after the shaders are compiled.

//Get the handles
textureU = glGetUniformLocation(program,"texture");
tintU = glGetUniformLocation(program,"tint");
viewMatrixU = glGetUniformLocation(program,"viewMatrix");
transformMatrixU = glGetUniformLocation(program,"transformMatrix");
positionA = glGetAttribLocation(program,"position");
texcoordA = glGetAttribLocation(program,"texcoord");

//Detect if this shader can handle textures
if(texcoordA < 0 || textureU < 0) hasTexture = false;
else hasTexture = true;

//Enable Attributes
glEnableVertexAttribArray(positionA);
if(hasTexture) glEnableVertexAttribArray(texcoordA);

If I am rendering an item that is textured, each element in verts consists of 5 values (x,y,z,tx,ty), but if the item isn't textures, each element in verts contains only 3 values (x,y,z).

Here is the problem: When the first item rendered in the GL context does not have a texture, glDrawElements segfaults! However, if the first item rendered does have a texture, it works fine, and any untextured items after the textured one work fine (that is, until a new context is created).

This chunk of code renders an item

glBindBuffer(GL_ARRAY_BUFFER,engine->vertBuffer);
glBufferData(GL_ARRAY_BUFFER,sizeof(GLfloat)*item->verts.size(),&item->verts[0],GL_DYNAMIC_DRAW);

item->shader->SetShader();

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER,engine->elementBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER,sizeof(GLuint) * item->indicies.size(),&item->indicies[0],GL_DYNAMIC_DRAW);

if(item->usingTexture)
    item->shader->SetTexture(item->texture->handle);

glUniformMatrix4fv(item->shader->transformMatrixU,1,GL_TRUE,&item->matrix.contents[0]);
glUniformMatrix4fv(item->shader->viewMatrixU,1,GL_TRUE,&item->batch->matrix.contents[0]);
glUniform4f(item->shader->tintU,item->color.x,item->color.y,item->color.z,item->color.w);

glDrawElements(GL_TRIANGLES,item->indicies.size(),GL_UNSIGNED_INT,0); //segfault

Here is the function seen above that sets the shader.

glUseProgram(program); currentShader = program;
GLsizei stride = 12;
if(hasTexture) stride = 20;
glVertexAttribPointer(positionA,3,GL_FLOAT,GL_FALSE,stride,0);
if(hasTexture)
    glVertexAttribPointer(texcoordA,2,GL_FLOAT,GL_FALSE,stride,(void*)12);

As far as I know, this problem is not apparent on Intel Integrated Graphics, which seem to be quite lenient.

Edit: If it is useful to know, I am using GLFW and GLEW.

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2 回答 2

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尝试glDisableVertexAttribArray()在您的绘图调用后添加相应的 s：

glEnableVertexAttribArray(positionA);
if(hasTexture) glEnableVertexAttribArray(texcoordA);
// draw
glDisableVertexAttribArray(positionA);
if(hasTexture) glDisableVertexAttribArray(texcoordA);
于 2013-01-12T10:29:35.247 回答
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问题是我在编译着色器后启用了顶点属性数组。这不是我应该启用它们的地方。

我在编译着色器时启用了 texcoord 属性，但由于第一项没有使用它，glDrawElements 会出现段错误。

我通过在设置着色器时启用该属性来解决此问题。

于 2013-01-12T21:32:39.327 回答