VBO与立即模式（glBegin / glEnd）的行为是否存在任何行为差异？ [英] Should there be any behavioural differece in behaviour for VBO vs immediate mode (glBegin/glEnd)?

问题描述

我的主要渲染循环是：

  //清除颜色和深度缓冲区
 glClear（GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT）; 
 //重置转换
 glLoadIdentity（）; 
 //设置摄像机
 gluLookAt（x，1.0f，z，
 x + lx，1.0f，z + lz，
 0.0f，1.0f，0.0f） ; 
 //绘制地面
 glColor3f（0.9f，0.9f，0.9f）; 
 glBegin（GL_QUADS）; 
 glVertex3f（-100.0f，0.0f，-100.0f）; 
 glVertex3f（ -  100.0f，0.0f，100.0f）; 
 glVertex3f（100.0f，0.0f，100.0f）; 
 glVertex3f（100.0f，0.0f，-100.0f）; 
 glEnd（）; 
 //绘制三角形
 glColor3f（0.9f，0.2f，0.1f）; 
 glRotatef（angle，0.0f，1.0f，0.0f）; 
 if（vboTest）vboTest-> draw（）; 
 / *上面的> draw（）将等价于
到下面的立即模式
 glBegin（GL_TRIANGLES）; 
 glVertex3f（-1.0f，0.2f，-1.0f）; 
 glVertex3f（-1.0f，0.2f，1.0f）; 
 glVertex3f（1.0f，0.2f，1.0f）; 
 glEnd（）; * / 
  

包含在 vboTest 使用与上述注释代码完全相同的值初始化，但是当我使用以下代码呈现它时：

  // bind顶点和索引
 glBindBuffer（GL_ARRAY_BUFFER，vbos_ [0]）; // vertexes 
 glBindBuffer（GL_ELEMENT_ARRAY_BUFFER，vbos_ [2]）; // indices 
 //与顶点数组相同，除了指针
 glEnableClientState（GL_VERTEX_ARRAY）; // activate vertex coords array 
 glVertexPointer（3，GL_FLOAT，0，0）; // last param is offset，not ptr 
 //使用索引数组的偏移量绘制n​​_tris_三角形
 glDrawElements（GL_TRIANGLES，n_vertex_，GL_UNSIGNED_INT，0）; 
 //停用顶点数组
 glDisableClientState（GL_VERTEX_ARRAY）; 
 //绑定为0，因此，切换回正常的指针操作
 glBindBuffer（GL_ARRAY_BUFFER，0）; 
 glBindBuffer（GL_ELEMENT_ARRAY_BUFFER，0）; 
  

三角形似乎旋转，但在旋转时发生变形。< br>当然，如果我要使用上面的立即模式代码，我可以看到一个旋转三角形没有问题。

t VBO应该在语义上等效于立即模式吗？

解决方案

>令人惊讶的是，在顶点声明期间，我缺少一个逗号。
我不敢相信：

  GLfloat v [] = {-1.0f，0.2f，-1.0 f //逗号丢失这里！ 
 -1.0f，0.2f，1.0f，
 1.0f，0.2f，1.0f}; 
  

几乎与
我是无语的！

干杯，

E

I have a sample code which initialize a VBO with a triangle and then renders it.

My main rendering loop is:

// Clear Color and Depth Buffers
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// Reset transformations
glLoadIdentity();
// Set the camera
gluLookAt(  x, 1.0f, z,
            x+lx, 1.0f,  z+lz,
            0.0f, 1.0f,  0.0f);
// Draw ground
glColor3f(0.9f, 0.9f, 0.9f);
glBegin(GL_QUADS);
    glVertex3f(-100.0f, 0.0f, -100.0f);
    glVertex3f(-100.0f, 0.0f,  100.0f);
    glVertex3f( 100.0f, 0.0f,  100.0f);
    glVertex3f( 100.0f, 0.0f, -100.0f);
glEnd();
// draw triangle
glColor3f(0.9f, 0.2f, 0.1f);
glRotatef(angle, 0.0f, 1.0f, 0.0f);
if(vboTest) vboTest->draw();
/* The above ->draw() would be equivalent
to the following immediate mode
glBegin(GL_TRIANGLES);
    glVertex3f(-1.0f, 0.2f, -1.0f);
    glVertex3f(-1.0f, 0.2f,  1.0f);
    glVertex3f( 1.0f, 0.2f,  1.0f);
glEnd();*/

The data contained in vboTest is initialized with exactly the same values as the commented code above, but then when I render it with following code

// bind vertexes and indexes
glBindBuffer(GL_ARRAY_BUFFER, vbos_[0]); // vertexes
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbos_[2]); // indexes
// do same as vertex array except pointer
glEnableClientState(GL_VERTEX_ARRAY); // activate vertex coords array
glVertexPointer(3, GL_FLOAT, 0, 0); // last param is offset, not ptr
// draw n_tris_ triangles using offset of index array
glDrawElements(GL_TRIANGLES, n_vertex_, GL_UNSIGNED_INT, 0);
// deactivate vertex array
glDisableClientState(GL_VERTEX_ARRAY);            
// bind with 0, so, switch back to normal pointer operation
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

The triangle appear to be rotating but is being deformed whilst spinning.
Of course, if I'm to use the immediate mode code above, I can see a spinning triangle without issues.

Aren't VBO supposed to behave semantically equivalent immediate mode? What am I doing wrong?

解决方案

I found the issue!

Surprisingly, during vertex declarations, I was missing one comma. I can't believe it:

GLfloat v[] = { -1.0f, 0.2f, -1.0f // comma missing here!
                -1.0f, 0.2f,  1.0f,
                1.0f, 0.2f,  1.0f };

Almost the same as this question.
I'm speechless!

Cheers,
E

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