OpenGL中的多维数据集的纹理坐标是什么? [英] What are the texture coordinates for a cube in OpenGL?

问题描述

我有一个定义为的多维数据集:

I have a cube defined as:

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
        };  

，我有图像128x128，我只想在多维数据集的6个面上分别绘画，就别无其他.那么什么是纹理坐标呢?我需要实际值.

and I have image 128x128 which I simply want to be painted on each of the 6 faces of the cube and nothing else. So what are the texture cooridinates? I need the actual values.

这是绘图代码:

// 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, mVerticesBuffer);


            // Bind the texture according to the set texture filter
            gl.glBindTexture(GL10.GL_TEXTURE_2D, textures[filter]);
            gl.glEnable(GL10.GL_TEXTURE_2D);



            // Enable the texture state
            gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY);

            // Point to our buffers
            gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, mTextureBuffer);



        // Set flat color
        gl.glColor4f(red, green, blue, alpha);


        gl.glDrawElements(GL10.GL_TRIANGLES, mNumOfIndices,
                GL10.GL_UNSIGNED_SHORT, mIndicesBuffer);

        // ALL the DRAWING IS DONE NOW

        // Disable the vertices buffer.
        gl.glDisableClientState(GL10.GL_VERTEX_ARRAY);


            gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY);


        // Disable face culling.
        gl.glDisable(GL10.GL_CULL_FACE);

这是索引数组:

short indices[] = { 0, 2, 1,
                0, 3, 2,

                1,2,6,
                6,5,1,

                4,5,6,
                6,7,4,

                2,3,6,
                6,3,7,

                0,7,3,
                0,4,7,

                0,1,5,
                0,5,4


               };  

我不确定是否需要索引数组才能找到tex坐标.请注意，我给出的多维数据集顶点数组是使用索引数组最有效地表示多维数据集.立方体绘制完美，但纹理绘制不完美.只有一侧显示正确的图像，而另一侧则混乱.我使用了各种有关纹理的在线教程中介绍的方法，但是它不起作用.

I am not sure if index array is needed to find tex coordinates. Note that the cube vertex array I gave is the most efficient representation of a cube using the index array. The cube draws perfectly but not the textures. Only one side shows correct picture but other sides are messed up. I used the methods described in various online tutorials on textures but it does not work.

推荐答案

您正在寻找的是一个多维数据集地图.在OpenGL中，您可以一次定义六个纹理(代表一个立方体的大小边)，并使用3D纹理坐标而不是普通的2D纹理坐标进行映射.对于简单的立方体，纹理坐标将与顶点的相应法线相同. (如果仅以这种方式对平面立方体进行纹理化，则也可以在顶点着色器中合并法线和纹理坐标！)与尝试将相同纹理应用于重复四边形相比，立方体贴图要简单得多(额外的不必要的绘制步骤).

What you are looking for is a cube map. In OpenGL, you can define six textures at once (representing the size sides of a cube) and map them using 3D texture coordinates instead of the common 2D texture coordinates. For a simple cube, the texture coordinates would be the same as the vertices' respective normals. (If you will only be texturing plane cubes in this manner, you can consolidate normals and texture coordinates in your vertex shader, too!) Cube maps are much simpler than trying to apply the same texture to repeating quads (extra unnecessary drawing steps).

GLuint mHandle;
glGenTextures(1, &mHandle); // create your texture normally

// Note the target being used instead of GL_TEXTURE_2D!
glTextParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTextParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);
glTextParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTextParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glBindTexture(GL_TEXTURE_CUBE_MAP, mHandle);

// Now, load in your six distinct images. They need to be the same dimensions!
// Notice the targets being specified: the six sides of the cube map.
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X, 0, GL_RGBA, width, height, 0,
    format, GL_UNSIGNED_BYTE, data1);
glTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_X, 0, GL_RGBA, width, height, 0,
    format, GL_UNSIGNED_BYTE, data2);
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_Y, 0, GL_RGBA, width, height, 0,
    format, GL_UNSIGNED_BYTE, data3);
glTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_Y, 0, GL_RGBA, width, height, 0,
    format, GL_UNSIGNED_BYTE, data4);
glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_Z, 0, GL_RGBA, width, height, 0,
    format, GL_UNSIGNED_BYTE, data5);
glTexImage2D(GL_TEXTURE_CUBE_MAP_NEGATIVE_Z, 0, GL_RGBA, width, height, 0,
    format, GL_UNSIGNED_BYTE, data6);

glGenerateMipmap(GL_TEXTURE_CUBE_MAP);
glTextParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);

// And of course, after you are all done using the textures...
glDeleteTextures(1, &mHandle);

指定纹理坐标时，将使用3个坐标集而不是2个坐标集.在一个简单的立方体中，使用归一化矢量指向8个角.如果N = 1.0/sqrt(3.0)，则一个角将为N，N，N；否则，一个角将为N，N，N.另一个是N，N，-N;等

When specifying your texture coordinates, you will then use sets of 3 coordinates instead of sets of 2. In a simple cube, you point to the 8 corners using normalized vectors. If N = 1.0 / sqrt(3.0) then one corner would be N, N, N; another would be N, N, -N; etc.

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