openGL 中使用三角形的天空盒

Question

我正在尝试在 openGL 中实现一个天空盒，但由于某种原因，除非我关闭背面剔除，否则它无法正确绘制，即使如此，它也会显示 3 个搞砸的三角形。玛比，我没有画对三角形，但我不确定。

bool Skybox::onInitialize()
{
    myRadius = 100;
    setPosition(Vector3(0.0f, 0.0f, 0.0f));

    //Initialize color matrix
    myColors.push_back(Color(1.0f, 0.0f, 0.0f, 1.0f));
    myColors.push_back(Color(1.0f, 1.0f, 0.0f, 1.0f));
    myColors.push_back(Color(1.0f, 0.5f, 0.0f, 1.0f));
    myColors.push_back(Color(0.5f, 0.5f, 0.5f, 1.0f));

    //Position the key points of the cube
    myVertices.push_back(Vertex(-myRadius, -myRadius,  myRadius));//0
    myVertices.push_back(Vertex(-myRadius, -myRadius, -myRadius));//1
    myVertices.push_back(Vertex(myRadius, -myRadius, -myRadius));//2
    myVertices.push_back(Vertex(myRadius, -myRadius,  myRadius));//3

    myVertices.push_back(Vertex(-myRadius, myRadius,  myRadius));//4
    myVertices.push_back(Vertex(-myRadius, myRadius, -myRadius));//5
    myVertices.push_back(Vertex( myRadius, myRadius, -myRadius));//6
    myVertices.push_back(Vertex( myRadius, myRadius,  myRadius));//7

    //Push back the indices that make up the triangles for each face.
    //Bottom
    myIndices.push_back(0);
    myIndices.push_back(1);
    myIndices.push_back(2);
    myIndices.push_back(2);
    myIndices.push_back(1);
    myIndices.push_back(0);

    //Top
    myIndices.push_back(7);
    myIndices.push_back(6);
    myIndices.push_back(4);
    myIndices.push_back(6);
    myIndices.push_back(5);
    myIndices.push_back(4);

    //Left
    myIndices.push_back(0);
    myIndices.push_back(4);
    myIndices.push_back(1);
    myIndices.push_back(4);
    myIndices.push_back(5);
    myIndices.push_back(1);

    //Right
    myIndices.push_back(2);
    myIndices.push_back(6);
    myIndices.push_back(3);
    myIndices.push_back(6);
    myIndices.push_back(7);
    myIndices.push_back(3);

    //Back
    myIndices.push_back(6);
    myIndices.push_back(1);
    myIndices.push_back(5);
    myIndices.push_back(6);
    myIndices.push_back(2);
    myIndices.push_back(1);

    //Front
    myIndices.push_back(0);
    myIndices.push_back(7);
    myIndices.push_back(4);
    myIndices.push_back(0);
    myIndices.push_back(3);
    myIndices.push_back(7);

    //Generate Texture Coordinates
    //Bottom
    myTexCoords.push_back(TexCoord(0.25, 0));
    myTexCoords.push_back(TexCoord(0.25, 0.375));
    myTexCoords.push_back(TexCoord(0.5, 0.375));
    myTexCoords.push_back(TexCoord(0.5, 0));

    //Top
    myTexCoords.push_back(TexCoord(0.25, 1));
    myTexCoords.push_back(TexCoord(0.25, 0.625));
    myTexCoords.push_back(TexCoord(0.5, 0.625));
    myTexCoords.push_back(TexCoord(0.5, 1));

    //Left
    myTexCoords.push_back(TexCoord(0, 0.625));
    myTexCoords.push_back(TexCoord(0.25, 0.625));
    myTexCoords.push_back(TexCoord(0.25, 0.375));
    myTexCoords.push_back(TexCoord(0, 0.375));

    //Right
    myTexCoords.push_back(TexCoord(0.5, 0.625));
    myTexCoords.push_back(TexCoord(0.75, 0.625));
    myTexCoords.push_back(TexCoord(0.75, 0.375));
    myTexCoords.push_back(TexCoord(0.5, 0.375));

    //Back
    myTexCoords.push_back(TexCoord(0.75, 0.625));
    myTexCoords.push_back(TexCoord(1.0, 0.625));
    myTexCoords.push_back(TexCoord(1.0, 0.375));
    myTexCoords.push_back(TexCoord(0.75, 0.375));

    const string vertexShader = (GLSLProgram::glsl130Supported()) ? VERTEX_SHADER_130 : VERTEX_SHADER_120;
    const string fragmentShader = (GLSLProgram::glsl130Supported()) ? FRAGMENT_SHADER_130 : FRAGMENT_SHADER_120;

    if (!myTexture.load(SKY_TEXTURE))
    {
        std::cerr << "Could not load the particle texture" << std::endl;
        return false;
    }

    glGenTextures(1, &myTexID);
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, myTexID);

    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, myTexture.getWidth(),
        myTexture.getHeight(), 0, GL_RGBA, GL_UNSIGNED_BYTE,
        myTexture.getImageData());


    m_shaderProgram = std::auto_ptr<GLSLProgram>(new GLSLProgram(vertexShader, fragmentShader));

    if (!m_shaderProgram->initialize())
    {
        std::cerr << "Could not load the skybox shaders" << std::endl;
        return false;
    }

    m_shaderProgram->bindAttrib(0, "a_Vertex");
    m_shaderProgram->bindAttrib(1, "a_Color");
    m_shaderProgram->bindAttrib(2, "a_TexCoord0");
    m_shaderProgram->linkProgram();
    m_shaderProgram->sendUniform("texture0", 0);

    glGenBuffers(1, &myVertexBuffer); //Generate a buffer for the vertices
    glBindBuffer(GL_ARRAY_BUFFER, myVertexBuffer); //Bind the vertex buffer
    glBufferData(GL_ARRAY_BUFFER, sizeof(Vector3) * myVertices.size(), &myVertices[0], GL_STATIC_DRAW); //Send the data to OpenGL

    glGenBuffers(1, &myColorBuffer);
    glBindBuffer(GL_ARRAY_BUFFER, myColorBuffer); 
    glBufferData(GL_ARRAY_BUFFER, sizeof(Color) * myColors.size(), &myColors[0], GL_STATIC_DRAW); //Send the data to OpenGL

    glGenBuffers(1, &myTexCoordBuffer); 
    glBindBuffer(GL_ARRAY_BUFFER, myTexCoordBuffer); 
    glBufferData(GL_ARRAY_BUFFER, sizeof(TexCoord) * myTexCoords.size(), &myTexCoords[0], GL_STATIC_DRAW); //Send the data to OpenGL

    glGenBuffers(1, &myIndexBuffer);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, myIndexBuffer); //Bind the vertex buffer
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint) * myIndices.size(), &myIndices[0], GL_STATIC_DRAW); //Send the data to OpenGL

    return true;
}

---

void Skybox::onRender() const
{
    //glDisable(GL_DEPTH_TEST);

    //glPushMatrix();
    glTranslatef(0.0f, 0.0f, 0.0f);
    static float modelviewMatrix[16];
    static float projectionMatrix[16];

    m_shaderProgram->bindShader();

    //Get the current matrices from OpenGL
    glGetFloatv(GL_MODELVIEW_MATRIX, modelviewMatrix);
    glGetFloatv(GL_PROJECTION_MATRIX, projectionMatrix);

    //Enable the point sprite and the automatic texture coordinates
    glBindTexture(GL_TEXTURE_2D, myTexID);

    glEnableVertexAttribArray(0);
    glEnableVertexAttribArray(1);
    glEnableVertexAttribArray(2);

    //Send the modelview and projection matrices to the shaders
    m_shaderProgram->sendUniform4x4("modelview_matrix", modelviewMatrix);
    m_shaderProgram->sendUniform4x4("projection_matrix", projectionMatrix);
    m_shaderProgram->sendUniform("texture0", 0);

    //Bind the vertex array and set the vertex pointer to point at it
    glBindBuffer(GL_ARRAY_BUFFER, myVertexBuffer);
    glVertexAttribPointer((GLint)0, 3, GL_FLOAT, GL_FALSE, 0, 0);

    glBindBuffer(GL_ARRAY_BUFFER, myColorBuffer);
    glVertexAttribPointer((GLint)1, 4, GL_FLOAT, GL_FALSE, 0, 0);

    glBindBuffer(GL_ARRAY_BUFFER, myTexCoordBuffer);
    glVertexAttribPointer((GLint)2, 2, GL_FLOAT, GL_FALSE, 0, 0);

    //Bind the index array
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, myIndexBuffer);


    //glDrawElements(GL_TRIANGLES, myIndices.size(), GL_UNSIGNED_INT, 0);
    glPointSize(5.0f);
    glDrawArrays(GL_TRIANGLES, 0, myIndices.size());

    glDisableVertexAttribArray(2);
    glDisableVertexAttribArray(1);
    glDisableVertexAttribArray(0);

   // glPopMatrix();
}

Answer 1

你的绘图代码非常混乱。它有很多问题，但它们都源于一个根本性的误解。

您有 4 种颜色、8 个位置和 24 个纹理坐标。 OpenGL 不知道该怎么办。

OpenGL 只能使用唯一的顶点属性组。因此，如果您有位置和纹理坐标，这些数组的长度必须相等。对于每个纹理坐标，都有一个与其配对的特定位置，反之亦然。对于每个位置，都有与其配对的特定颜色，反之亦然。

是的，一个立方体只有 8 个不同的位置。但您没有绘制 8 个顶点（顶点是属性数据的集合，如果您愿意，其中可能包含一个位置）。您正在绘制 12 个三角形。每个三角形有 3 个顶点。

仅当三角形共享该顶点的所有顶点属性时，三角形才能共享该顶点。因此，立方体的一个面可以由四个角顶点表示，因为两个三角形（沿着主对角线）对于两个共享顶点共享相同的位置/颜色/texCoord。

但不同面的三角形只有使用相同位置/颜色/texCoord 三元组才能共享顶点数据。在大多数情况下，你的不会。

因此，你必须大量复制你的位置和颜色。立方体的每个面都有独立的位置和颜色（即使它们可能使用与其他面相同的值）。

另外，请考虑完全避免纹理坐标。显然您正在使用着色器，因此只需将您的环境放入立方体贴图中即可。您可以在立方体贴图向外指向的 8 个角处传递“法线”。将它们作为标准进行插值，然后使用它们访问立方体贴图纹理。