使用多个顶点和索引缓冲区对象进行渲染 (ios - OpenGLES 2.0)

Question

我无法使用超过 1 对顶点和索引缓冲区对象来渲染我的所有对象。为了检查一切，我只初始化了 3 个对象并渲染它们。这会导致前两个对象的几何图形失真，而第三个对象的几何图形渲染得有些精细（不完美）。

当我只初始化所有 3 个但只先渲染时，它再次显示扭曲的几何图形，并且以某种方式第三个几何图形更明显（即使我没有渲染它）。

但是，如果我正在初始化和渲染其中任何一个，它就会呈现得很好（完美）。 这是我的代码：

float tempAngles[4] = {0, 60, 180, 360};
pieOne = [[IVNode alloc]initWithPieGeometry:0.75 thickness:0.20 startAngle:tempAngles[0]*M_PI/180   andEndAngle:tempAngles[1]*M_PI/180];

glGenBuffers(1, &vertexBuffer1);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer1);//vertexBuffer[i]);
glBufferData(GL_ARRAY_BUFFER, [pieOne.pie getVertexSize]*sizeof(GLfloat), [pieOne.pie returnVertexArray] , GL_STATIC_DRAW);

glGenBuffers(1, &indexBuffer1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer1);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, [pieOne.pie getIndicesSize]*sizeof(GLushort),[pieOne.pie returnIndexArray], GL_STATIC_DRAW);

pieTwo = [[IVNode alloc]initWithPieGeometry:1.0 thickness:0.20 startAngle:tempAngles[1]*M_PI/180 andEndAngle:tempAngles[2]*M_PI/180];

glGenBuffers(1, &vertexBuffer2);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer2);//vertexBuffer[i]);
glBufferData(GL_ARRAY_BUFFER, [pieTwo.pie getVertexSize]*sizeof(GLfloat), [pieTwo.pie returnVertexArray] , GL_STATIC_DRAW);

glGenBuffers(1, &indexBuffer2);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer2);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, [pieTwo.pie getIndicesSize]*sizeof(GLushort),[pieTwo.pie returnIndexArray], GL_STATIC_DRAW);


pieThree = [[IVNode alloc]initWithPieGeometry:0.75 thickness:0.20 startAngle:tempAngles[2]*M_PI/180 andEndAngle:tempAngles[3]*M_PI/180];

glGenBuffers(1, &vertexBuffer3);
glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer3);//vertexBuffer[i]);
glBufferData(GL_ARRAY_BUFFER, [pieThree.pie getVertexSize]*sizeof(GLfloat), [pieThree.pie returnVertexArray] , GL_STATIC_DRAW);

glGenBuffers(1, &indexBuffer3);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer3);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, [pieThree.pie getIndicesSize]*sizeof(GLushort),[pieThree.pie returnIndexArray], GL_STATIC_DRAW);

//#define BUFFER_OFFSET(i) ((char *)NULL + (i))
glEnableVertexAttribArray(GLKVertexAttribPosition);
glVertexAttribPointer(GLKVertexAttribPosition, 3, GL_FLOAT, GL_FALSE, 6*sizeof(GLfloat), BUFFER_OFFSET(0));
glEnableVertexAttribArray(GLKVertexAttribNormal);
glVertexAttribPointer(GLKVertexAttribNormal, 3, GL_FLOAT, GL_FALSE, 6*sizeof(GLfloat), BUFFER_OFFSET(12));

现在在我的渲染函数中，我有：

-(void)glkView:(GLKView *)view drawInRect:(CGRect)rect
{

glClearColor(0.77f, 0.88f, 1.0f, 1.0f);     
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);


float yellow[3][4] = {1.0f, 1.0f, 0.0f, 1.0f,
    1.0f, 0.0f, 0.0f, 1.0f,
    1.0f, 1.0f, 1.0f, 1.0f};

glUseProgram(_program);
//1st   
GLKMatrix4 model = GLKMatrix4Identity;// GLKMatrix4MakeTranslation(1.5, 0, 0);
_modelViewProjectionMatrix = GLKMatrix4Multiply(_modelViewProjectionMatrix, model);

glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glUniformMatrix3fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, 0,_normalMatrix.m);
glUniform4f(uniforms[COLOR_VECTOR], yellow[0][0], yellow[0][1], yellow[0][2], yellow[0][3]);   

//bind corresponding buffer before drawing
glBindBuffer(GL_ARRAY_BUFFER, indexBuffer1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer1);
glDrawElements(GL_TRIANGLES, [pieOne.pie getIndicesSize], GL_UNSIGNED_SHORT, (void*)0);

//2nd    
model = GLKMatrix4MakeTranslation(0, -1, 0);
_modelViewProjectionMatrix = GLKMatrix4Multiply(_modelViewProjectionMatrix, model);

glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glUniformMatrix3fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, 0,_normalMatrix.m);//
glUniform4f(uniforms[COLOR_VECTOR], yellow[1][0], yellow[1][1], yellow[1][2], yellow[1][3]);   

//bind corresponding buffer before drawing
glBindBuffer(GL_ARRAY_BUFFER, indexBuffer2);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer2);
glDrawElements(GL_TRIANGLES, [pieTwo.pie getIndicesSize], GL_UNSIGNED_SHORT,(void*)0);

//3rd
model = GLKMatrix4MakeTranslation(-1.5, 0, 0);
_modelViewProjectionMatrix = GLKMatrix4Multiply(_modelViewProjectionMatrix, model);
glUniformMatrix4fv(uniforms[UNIFORM_MODELVIEWPROJECTION_MATRIX], 1, 0, _modelViewProjectionMatrix.m);
glUniformMatrix3fv(uniforms[UNIFORM_NORMAL_MATRIX], 1, 0,_normalMatrix.m);
glUniform4f(uniforms[COLOR_VECTOR], yellow[2][0], yellow[2][1], yellow[2][2], yellow[2][3]);   

//bind corresponding buffer before drawing
glBindBuffer(GL_ARRAY_BUFFER, indexBuffer3);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer3);
glDrawElements(GL_TRIANGLES, [pieThree.pie getIndicesSize], GL_UNSIGNED_SHORT, (void*)0);

}

getIndicesSize 返回 indexArray 中元素的数量。 getVertexSize 返回 vertexArray 中的元素个数。 returnVertexArray 返回几何的顶点数组。 returnIndexArray 返回几何的索引数组。 顶点数组的类型为 GLfloat。 索引数组的类型是 GLushort。

生成的顶点数组中的元素数为 24522。 生成的索引数组中的元素数为 22680。 在互联网上，我发现只有多个 VBO/IBO 的示例没有使用 GLkit，它们在初始化缓冲区和渲染方面完全按照我在这里所做的。 我在这个问题上花了将近 2 天的时间。我觉得缺少一些非常基本的东西。不知何故，最后一个绑定缓冲区会影响我感觉到的所有其他几何图形（基于我上面解释的结果）。可能是模拟器问题（我不这么认为）？快速响应将不胜感激。谢谢

Answer 1

您似乎对glVertexAttribPointer 函数的工作方式有些困惑。当你调用glVertexAttribPointer时，它告诉OpenGL：

在下一次绘制调用中，从当前绑定缓冲区的地址加上提供的缓冲区偏移量开始渲染。

在此之后，更改绑定的缓冲区无关紧要，因为指针仍然指向函数调用时绑定的缓冲区。

因此在这段代码中：

glBindBuffer(GL_ARRAY_BUFFER, indexBuffer1);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer1);
glDrawElements(GL_TRIANGLES, [pieOne.pie getIndicesSize], GL_UNSIGNED_SHORT, (void*)0);

调用 glBindBuffer(GL_ARRAY_BUFFER) 在这里绝对没有任何作用，因为您没有更新指针。

glBindBuffer(GL_ARRAY_BUFFER, indexBuffer1);
//need to set glVertexAttribPointers here
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer1);
glDrawElements(GL_TRIANGLES, [pieOne.pie getIndicesSize], GL_UNSIGNED_SHORT, (void*)0);