OpenGL ES - 纹理贴图 8 个顶点立方体的所有面? [英] OpenGL ES - texture map all faces of an 8 vertex cube?
问题描述
使用 Android 模拟器完成一些 OpenGL-ES 教程.我已经掌握了纹理映射，但在映射到立方体时遇到了一些麻烦.是否可以将纹理映射到具有 8 个顶点和 6 个面的 12 个三角形的立方体的所有面，如下所述?
Working through some OpenGL-ES tutorials, using the Android emulator. I've gotten up to texture mapping and am having some trouble mapping to a cube. Is it possible to map a texture to all faces of a cube that has 8 vertices and 12 triangles for the 6 faces as described below?
// Use half as we are going for a 0,0,0 centre.
width /= 2;
height /= 2;
depth /= 2;
float vertices[] = { -width, -height, depth, // 0
width, -height, depth, // 1
width, height, depth, // 2
-width, height, depth, // 3
-width, -height, -depth, // 4
width, -height, -depth, // 5
width, height, -depth, // 6
-width, height, -depth, // 7
};
short indices[] = {
// Front
0,1,2,
0,2,3,
// Back
5,4,7,
5,7,6,
// Left
4,0,3,
4,3,7,
// Right
1,5,6,
1,6,2,
// Top
3,2,6,
3,6,7,
// Bottom
4,5,1,
4,1,0,
};
float texCoords[] = {
1.0f, 1.0f,
0.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
1.0f, 1.0f,
0.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
1.0f, 1.0f,
0.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
1.0f, 1.0f,
0.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
1.0f, 1.0f,
0.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
1.0f, 1.0f,
0.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
};
我的正面和背面都可以正常工作，但是，其他面都没有显示纹理.
I have gotten the front and back faces working correctly, however, none of the other faces are showing the texture.
绘图代码
public void draw(GL10 gl) {
// Counter-clockwise winding.
gl.glFrontFace(GL10.GL_CCW);
// Enable face culling.
gl.glEnable(GL10.GL_CULL_FACE);
// What faces to remove with the face culling.
gl.glCullFace(GL10.GL_BACK);
// Enabled the vertices buffer for writing and to be used during
// rendering.
gl.glEnableClientState(GL10.GL_VERTEX_ARRAY);
// Specifies the location and data format of an array of vertex
// coordinates to use when rendering.
gl.glVertexPointer(3, GL10.GL_FLOAT, 0, verticesBuffer);
if (normalsBuffer != null) {
// Enabled the normal buffer for writing and to be used during rendering.
gl.glEnableClientState(GL10.GL_NORMAL_ARRAY);
// Specifies the location and data format of an array of normals to use when rendering.
gl.glNormalPointer(GL10.GL_FLOAT, 0, normalsBuffer);
}
// Set flat color
gl.glColor4f(rgba[0], rgba[1], rgba[2], rgba[3]);
// Smooth color
if ( colorBuffer != null ) {
// Enable the color array buffer to be used during rendering.
gl.glEnableClientState(GL10.GL_COLOR_ARRAY);
// Point out the where the color buffer is.
gl.glColorPointer(4, GL10.GL_FLOAT, 0, colorBuffer);
}
// Use textures?
if ( textureBuffer != null) {
gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
gl.glEnable(GL10.GL_TEXTURE_2D);
gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer);
}
// Translation and rotation before drawing
gl.glTranslatef(x, y, z);
gl.glRotatef(rx, 1, 0, 0);
gl.glRotatef(ry, 0, 1, 0);
gl.glRotatef(rz, 0, 0, 1);
gl.glDrawElements(GL10.GL_TRIANGLES, numOfIndices, GL10.GL_UNSIGNED_SHORT, indicesBuffer);
// Disable the vertices buffer.
gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);
gl.glDisableClientState(GL10.GL_COLOR_ARRAY);
gl.glDisableClientState(GL10.GL_NORMAL_ARRAY);
gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);
// Disable face culling.
gl.glDisable(GL10.GL_CULL_FACE);
}
推荐答案
你必须使用 24 个顶点.在 OpenGL 中，顶点不仅仅是位置，它是所有顶点属性的集合.每个顶点数组都使用相同的索引访问.
You have to use 24 vertexes. In OpenGL, a vertex is more than just position, it is the collection of all vertex attributes. Every vertex array is accessed with the same index.
臭名昭著的立方体示例在开始使用 OpenGL 时几乎每个人都觉得效率低下，但在现实世界中，更复杂的模型中，重复度非常低.
The infamous cube example is something almost everyone feels is inefficient when starting to use OpenGL, but in real-world, more complex models, the degree of duplication is quite low.
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