Opengl 翻译/旋转来自同一缓冲区的单个对象

Question

我尝试在 C + OpenGL 3.3 中编写一个简单的工业机器人手臂。我在单个缓冲区元素（顶点、索引和颜色缓冲区）中设置了 3 个简单模型，我可以旋转/平移整个东西。但是，我无法翻译/旋转单个部分。

顶点数据保存在 HEADER 文件中。红色段称为“base”，蓝色为“seg1”，绿色为“seg2”。我像这样将它们加载到缓冲区中。

size = sizeof(base_verticies) + sizeof(seg1_verticies) + sizeof(seg2_verticies);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, size, 0, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(base_verticies), base_verticies);
glBufferSubData(GL_ARRAY_BUFFER, sizeof(base_verticies), sizeof(seg1_verticies), seg1_verticies);
glBufferSubData(GL_ARRAY_BUFFER, sizeof(base_verticies)+sizeof(seg1_verticies), sizeof(seg2_verticies), seg2_verticies);

size = sizeof(base_indices) + sizeof(seg1_indices) + sizeof(seg2_indices);
glGenBuffers(1, &IBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, size, 0, GL_STATIC_DRAW);
glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, 0, sizeof(base_indices), base_indices);
glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, sizeof(base_indices), sizeof(seg1_indices), seg1_indices);
glBufferSubData(GL_ELEMENT_ARRAY_BUFFER, sizeof(base_indices)+sizeof(seg1_indices), sizeof(seg2_indices), seg2_indices);

size = sizeof(base_colors) + sizeof(seg1_colors) + sizeof(seg2_colors);
glGenBuffers(1, &CBO);
glBindBuffer(GL_ARRAY_BUFFER, CBO);
glBufferData(GL_ARRAY_BUFFER, size, 0, GL_STATIC_DRAW);
glBufferSubData( ... ); ...; // same for colors

我现在可以像这样单独绘制这些部分

//base (red)
glDrawElements(GL_TRIANGLES, sizeof(base_indices)/sizeof(GLushort), GL_UNSIGNED_SHORT, 0); 
//seg1 (blue)
glDrawElements(GL_TRIANGLES, sizeof(base_indices)/sizeof(GLushort), GL_UNSIGNED_SHORT, (void*)sizeof(base_indices));
//seg2 (green)
glDrawElements(GL_TRIANGLES, sizeof(base_indices)/sizeof(GLushort), GL_UNSIGNED_SHORT, (void*)(sizeof(base_indices)+sizeof(seg1_indices)));

但我的问题是，我只能旋转和翻译整个内容，而不是单个部分。我确实像这样在onIdle() 函数中旋转整个模型：

float angle = 1;
float RotationMatrixAnim[16];
SetRotationY(angle, RotationMatrixAnim);

/* Apply model rotation */
MultiplyMatrix(RotationMatrixAnim, InitialTransform, ModelMatrix);
MultiplyMatrix(TranslateDown, ModelMatrix, ModelMatrix);

1. 有没有办法修改单个句段的位置、翻译、...？我发现的唯一教程来自带有 glPushMatrix() 和 glPopMatrix 的旧版 OpenGL，它们已被弃用。

2. 将这些 Segment 存储在同一个缓冲区中是否是个好主意？

提前感谢您的帮助和宝贵的时间。

Answer 1

感谢 @Rabbid76 的建议，我能够解决我的问题。

1. 我制作了 3 个模型矩阵，每个部分一个

   float ModelMatrix[3][16]; /* Model matrix */
   

2. 我像这样旋转/翻译我想要的部分

   float RotationMatrixSeg2[16];
   SetRotationY(angle, RotationMatrixSeg2);
   
   MultiplyMatrix(RotationMatrixSeg2, InitialTransform, ModelMatrix[2]);
   MultiplyMatrix(TranslateDown, ModelMatrix[2], ModelMatrix[2]);
   

3. 我在绘制截面之前设置了对应的ModelMatrix。

   /* Draw each section */
   glUniformMatrix4fv(RotationUniform, 1, GL_TRUE, ModelMatrix[0]);
   glDrawElements(GL_TRIANGLES, sizeof(base_indices)/sizeof(GLushort), GL_UNSIGNED_SHORT, 0); 
   
   glUniformMatrix4fv(RotationUniform, 1, GL_TRUE, ModelMatrix[1]);
   glDrawElements(GL_TRIANGLES, sizeof(base_indices)/sizeof(GLushort), GL_UNSIGNED_SHORT, (void*)sizeof(base_indices));
   
   glUniformMatrix4fv(RotationUniform, 1, GL_TRUE, ModelMatrix[2]);
   glDrawElements(GL_TRIANGLES, sizeof(base_indices)/sizeof(GLushort), GL_UNSIGNED_SHORT, (void*)(sizeof(base_indices)+sizeof(seg1_indices)));