OpenGL ES glTexImage2D优化

Question

我的任务是展示几张照片。我将其实现为一个类来创建几个实例。每个实例表示一幅图片。它编译着色器，设置两个三角形，并在构造函数中加载图片数据。主程序创建实例，然后转到循环，为每个实例切换prigramid和调用render()方法。

while(true)
    for (uint g = 0; g < pictures.size(); g++){
        glUseProgram(pictures[g]->ProgramId);
        pictures[g]->render();
    }

它运行良好，并显示图片，但我不喜欢它。可以做得更好。

下面是类的部分代码

Picture::Picture(picPosition* pPosition, const char * fileName)
:BasePicture(pPosition)
{
    pos = glGetAttribLocation(ProgramId, "position");
    uv = glGetAttribLocation(ProgramId, "texture_vert");

    glGenBuffers(1, &vbo);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);

    glGenBuffers(1, &uvbuffer);
    glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);

    int n;
    textureData = stbi_load(fileName, &picWidth, &picHeight, &n, STBI_rgb_alpha);
    TextureID  = glGetUniformLocation(ProgramId, "myTextureSampler");
    glBindTexture(GL_TEXTURE_2D, TextureID);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glActiveTexture(GL_TEXTURE0);

    glDepthMask(GL_FALSE);
    glEnable(GL_BLEND);
    glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
    //calculating the vertex matrix using MVP calculated in parent class
    for (int i = 0; i < 6; i++)
        ModeledVerts.push_back(MVP * verts[i]);
    v = glm::value_ptr(ModeledVerts[0]);
}

Picture::~Picture()
{
    stbi_image_free(textureData);
    glDeleteBuffers(1, &vbo);
    glDeleteBuffers(1, &uvbuffer);
}

void Picture::render()
{
    glBufferData(GL_ARRAY_BUFFER, 96, v, GL_STATIC_DRAW);
    glVertexAttribPointer(pos, 4, GL_FLOAT, GL_FALSE, 0, (GLvoid*) 0);
    glEnableVertexAttribArray(pos);
    glBindBuffer(GL_ARRAY_BUFFER, vbo);

    glBufferData(GL_ARRAY_BUFFER, sizeof(verticesUV), verticesUV, GL_STATIC_DRAW);
    glVertexAttribPointer(uv, 2, GL_FLOAT, GL_FALSE, 0, (GLvoid*) 0);
    glEnableVertexAttribArray(uv);
    glBindBuffer(GL_ARRAY_BUFFER, uvbuffer);

    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, picWidth, picHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, textureData);

    glDrawArrays(GL_TRIANGLES, 0, 6);
}

我经常使用代码来使render()函数尽可能轻巧，但我不能使它比现在更轻。

最大的问题是每次发送textureData (glTexImage2D)。数据从未改变过。我试图将其移动到构造函数，但在本例中，所有图片对象都显示了最新加载的图片。看起来有一个实例覆盖了之前上传的纹理数据。我正在寻找一种方法来加载图片数据一次在构造函数，而不是每次它呈现。看起来这方面的OpenGL API中有一些东西，但我还不知道。

另一个改进是获取从render()中设置的顶点数据。数据永远不会变。但它并不像glTexImage2D在render()中调用的那样重要。

你能给我指一下OpenGL API来分离着色器的数据吗？或者告诉我我做错了什么。

Answer 1

回答我自己的问题。解决办法是使用地图集地图。软件生成包含所有图片的地图集，上传一次(glTexImage2D)并对每幅图片使用坐标。这大大提高了性能，因为只调用了一次glTexImage2D。

Answer 2

你说：

它运行良好，并显示图片，但我不喜欢它。可以做得更好。

从设计的角度来看，我认为这可能对你有帮助。

将打开、读取和解析纹理数据的图像文件的功能与实际的纹理结构或类分开。这将是一个示例伪代码：

struct Texture {
    unsigned int width;
    unsigned int height;
    bool         hasTransparency; 

    GLint id; // ID that is used by OpenGL to setActive, bind, and pass to shaders as either a uniform or sampler2D.
    std::string filenameAndPath; // Keep this filename associated with texture so you can prevent trying to reload the same file over and over.
    GLuchar*  data; // the actual color - pixel texture data. 
}

// This function will handle the opening and reading in of the texture data
// it would return back the ID value generated by OpenGL which will also be
// stored into the texture struct. The texture struct is returned by reference so that it can be populated with data.
GLuint loadTexture( const char* filenameAndPath, Texture& texture, /*loading parameters & flags*/ ) {
    // Check to see if file exists or is already loaded
    if ( fileanameAndPath already exists ) {
        // get the existing ID from the already loaded texture
        // and just return that. 
    } else {
        // Try to open the new file for reading.

        // parse the data for general purposes that will support
        // your application. You can simply use `stbi_load` as it is a fairly
        // decent third party library.

        // Check the internal formatting of how the data is stored
        // Compression, pixel orientation etc.

        // configure the data to your needs (color format),
        // (flipping the pixels either horizontally, vertically or both),

        // now copy the actual pixel data into your buffer.

        // close the file handle

        // save all the information into your struct

        // return the ID value that was generated by OpenGL
    }
}

在render loop之前的主引擎代码中，您需要从文件中加载纹理，然后您可以在需要的地方使用这个纹理对象。最后，在渲染循环中，您需要将纹理设置为活动，并将它们绑定到渲染目标，并将它们传递给您的着色器。在某些情况下，您可能希望将它们设置为active &在render loop之前绑定它们，具体取决于要实现的shader-technique类型。