图形学笔记 -- OpenGL 拷贝纹理的两种方式 & Texture storage format

Posted on April 7, 2021 (珠海)
图形学 OpenGL

一种是直观的使用 glGetTexImage，然后获取数据到内存再贴上去，这种方法很慢。

另一种是使用 FBO，将纹理附加到 FBO，然后用 glCopyTexSubImage2D，不涉及跟内存交换数据，速度飞快。

方法一：获取纹理再拷贝

unsigned char * data = new unsigned char[normal_texture.width*normal_texture.height*4];

glBindTexture(GL_TEXTURE_2D, src_id); // 绑定 src_id
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, data); // 下载到 data

glBindTexture(GL_TEXTURE_2D, dest_id); // 绑定 dest_id
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data); // 上传

glBindTexture(GL_TEXTURE_2D, 0);

第二种方法：FBO 拷贝

GLuint fbo;
glGenFramebuffers(1, &fbo);
// bind the FBO
glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo); // 绑定 FBO
    // attach the source texture to the fbo
    glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, src_id, 0); // 绑定纹理到 FBO
    // bind the destination texture
    glBindTexture(GL_TEXTURE_2D, dest_id); // 绑定 dest_id
        // copy from framebuffer (here, the FBO!) to the bound texture
        glCopyTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 0, 0, width, height); // 从 FBO 直接拷贝到 dest_id
    glBindTexture(GL_TEXTURE_2D, 0);
// unbind the FBO
glBindFramebuffer(GL_FRAMEBUFFER, 0);

TEXTURE_FORMAT.md

Texture storage format Wallpaper engine uses a custom texture storage format converted by resourcecompiler.exe

Information	Size	Default value
File type indicator	8 bytes	TEXV0005
Padding	1 byte	Null terminator for string
Extra file type indicator?	8 bytes	TEXI0001
Padding	1 byte	Null terminator for string
Texture type	1 byte	4 => DXT5? 0 => JPEG?
Unknown data	15 bytes	To be reversed
Width	4 bytes	Image's width
Height	4 bytes	Image's height
Unknown data	5 bytes	To be reversed
Container version	8 bytes	TEXB0003
Padding	1 byte	Null terminator for string
Unknown data	8 bytes	To be reversed
Mip map levels	4 bytes	The number of mipmaps stored for this texture
Mipmap entry	x bytes	See Mipmap entries

Mipmap entries

Information	Size	Default value
Width	4 bytes	Mipmap's entry width
Height	4 bytes	Mipmap's entry height
Compression flag	4 bytes	Indicates if the content is compressed or not
Next image size	4 bytes	Image block size (uncompressed)
Next image size	4 bytes	Image block size (compressed)
Mipmap pixels	x bytes	Actual bitmap data in the format specified

fakehookDebug.cpp

GLuint GetDebugTextureId() {
    static GLuint texture = 0;
    if (texture != 0) {
        return texture;
    }
    glGenTextures(1, &texture);
    glBindTexture(GL_TEXTURE_2D, texture);
    if (true) {
        GLubyte data[] = {
            255, 0, 0, 155,
            0, 255, 0, 155,
            0, 0, 255, 155,
            255, 255, 255, 155 };
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

        GLsizei width = 2;
        GLsizei height = 2;
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, data);
        glGenerateMipmap(GL_TEXTURE_2D);
    }
    glBindTexture(GL_TEXTURE_2D, 0);
    return texture;
}

参考资料快照

本文短链接：
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TEXTURE_FORMAT.md

Header

Mipmap entries

fakehookDebug.cpp