object - 一个不渲染的简单顶点缓冲区对象 (C++)

Question

我正在尝试使用 VBO 将普通的 2d 纹理正方形渲染到 FBO 上。立即模式功能可以完美运行，但 VBO 却不行。代码中已启用 GL_TEXTURE_2D。这是什么问题？

unsigned int VBOid = 0;
unsigned int Iid = 0;

float *geometry;
unsigned int *indices;

int num_geometry = 1;
int num_vertices = 4;
int num_indices = num_geometry*num_vertices;
geometry = new float[num_geometry*num_vertices*4];
indices = new unsigned int[num_indices];

indices[0] = 0;
indices[1] = 1;
indices[2] = 2;
indices[3] = 3;

/* Fill geometry: 0, 1, = vertex_xy
*                2, 3 = tex_coord_uv
*/
geometry[0] = 0.0f;
geometry[1] = 0.0f;
geometry[2] = 0.0f;
geometry[3] = 0.0f;

geometry[4] = 50.0f;
geometry[5] = 0.0f;
geometry[6] = 1.0f;
geometry[7] = 0.0f;

geometry[8] = 50.0f;
geometry[9] = 50.0f;
geometry[10] = 1.0f;
geometry[11] = 1.0f;

geometry[12] = 0.0f;
geometry[13] = 50.0f;
geometry[14] = 0.0f;
geometry[15] = 1.0f;

glGenBuffers(1, &VBOid);
glBindBuffer(GL_ARRAY_BUFFER, VBOid);
glBufferData(GL_ARRAY_BUFFER, sizeof(geometry), geometry, GL_STATIC_DRAW);

glGenBuffers(1, &Iid);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, Iid);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);

//GL_TEXTURE_2D is already enabled here
//Buffers are already bound from above

glBindTexture( GL_TEXTURE_2D, 2); //I used 2 just to test to see if it is rendering a texture correctly. Yes, 2 does exist in my program thats why i arbitrarily used it
//glClientActiveTexture(GL_TEXTURE0); I dont know what this is for and where to put it

glEnableClientState(GL_TEXTURE_COORD_ARRAY);
//glActiveTexture(GL_TEXTURE0); same here I dont know what this is for or where to put it
glVertexPointer(2, GL_FLOAT, sizeof(GLfloat)*4, 0);
glTexCoordPointer(2, GL_FLOAT, sizeof(GLfloat)*4, (float*)(sizeof(GLfloat)*2));

glDrawElements(GL_QUADS, num_indices, GL_UNSIGNED_INT, indices);

glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);

glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

Answer 1

问题是您在 glBufferData 调用中使用了 sizeof(geometry) (对于 indices 也是如此)。这些变量实际上只是指针，无论它们是否指向动态分配的数组(编译器不知道)。因此，您将始终获得指针的大小(4 或 8 字节，具体取决于平台)。

将 sizeof(geometry) 替换为 num_geometry*num_vertices*4*sizeof(float) 并将 sizeof(indices) 替换为 num_indices *sizeof(无符号整数)。好吧，事实上，您根本不需要任何索引，只需使用简单的即可绘制整个内容

glDrawArrays(GL_QUADS, 0, 4);

始终注意实际(编译时大小)数组与指向动态分配数组的单纯指针之间的差异，sizeof 运算符的结果是 one 这些差异(以及要求在稍后的某个时间点使用 delete[] 释放后者的内存是另一个但同样重要的差异)。