VBO什么都没画 [英] VBO doesn't draw anything

问题描述

我试图在我的本机Blackberry 10应用程序中使用VBO绘制一个正方形.我的实现是，

I am trying to draw a square with VBO in my native blackberry 10 application. My implementation is,

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_TEXTURE_2D);
    glEnableClientState(GL_VERTEX_ARRAY);
    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    glGenBuffers(1,&decompressTileImage->VBOId);
    glBindBuffer(GL_ARRAY_BUFFER,decompressTileImage->VBOId);
    glBufferData(GL_ARRAY_BUFFER,sizeof(tileCoordList)+sizeof(tileTextureCoordList),0,GL_STATIC_DRAW);
    glBufferSubData(GL_ARRAY_BUFFER,0,sizeof(tileCoordList),tileCoordList);
    glBufferSubData(GL_ARRAY_BUFFER,sizeof(tileCoordList),sizeof(tileTextureCoordList),tileTextureCoordList);

    glTexCoordPointer(3, GL_FLOAT, sizeof(tileTextureCoordList), (void*)sizeof(this->tileCoordList));
    glVertexPointer(3, GL_FLOAT, sizeof(tileCoordList), 0);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
    glDisable(GL_BLEND);
    glDisableClientState(GL_VERTEX_ARRAY);
    glDisableClientState(GL_TEXTURE_COORD_ARRAY);
    glDisable(GL_TEXTURE_2D);

    swapBuffers();

此处tileCoordList包含正方形的坐标，而tileTextureCoordList包含相应的纹理. tileCoordList是Square3D类型的结构.

Here tileCoordList contains the co-ordinates for the square and tileTextureCoordList contains the corresponding texture. tileCoordList is a Square3D type structure.

typedef struct
{
 Vertex3D lowerLeft;
 Vertex3D lowerRight;
 Vertex3D upperLeft;
 Vertex3D upperRight;
}Square3D;

typedef struct
{
GLfloat x;
GLfloat y;
GLfloat z;
} Vertex3D;

4 Vertex3D表示tileCoordList中的正方形. tileTextureCoordList也是如此.我可以在没有VBO的情况下进行罚款.我正在使用opengl-es 1.1

4 Vertex3D represents a square in tileCoordList. Same goes for tileTextureCoordList. I can draw fine without the VBO though. I am using opengl-es 1.1

另一个问题.

如果我创建两个VBO.假设我用它的ID绑定了第一个，并复制了数据并绘制了它.然后是第二个，我也将其绑定并复制数据并绘制它.现在，如果我想再次绘制第一个，是否需要再次绑定它?如果我需要再次绑定，是否还需要再次将数据复制到该VBO的缓冲区中?

If I create two VBOs. Suppose I bound the first one with its id and copied the data and drew it. And then comes the second one and I also bind it and copy the data and draw it. Now if I want to draw the first one again do I need to bind it again? If I need to bind again do I need to copy the data to buffer for that VBO again also?

推荐答案

注释中已经表明tileCoordList和tileTextureCoordList是指向Square3D结构的指针.

It has transpired in the comments that tileCoordList and tileTextureCoordListare pointers to Square3D structures.

这意味着sizeof运算符将为您提供指针的大小，而不是结构的大小.

This means that the sizeof operator will give you the size of a pointer, not the size of the struct.

您可以使用例如

glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(*tileCoordList), tileCoordList);

相反.

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