SOIL2加载灰度纹理异常：SOIL_LOAD_AUTO/LA显示黑块

问题现象 #

作为OpenGL初学者，使用SOIL2加载纹理时遇到以下问题：

• 使用SOIL_LOAD_AUTO或SOIL_LOAD_LA加载灰度纹理时，画面显示为黑块
• 使用SOIL_LOAD_RGBA时，纹理可正常显示

环境说明：OpenGL 3.3核心配置文件，启用向前兼容。曾排查灰度模式相关资料但未找到解决思路，附带完整渲染代码、Texture类代码、着色器代码及纹理图、错误/预期显示效果（此处略）。

原SOIL2加载代码 #

GLuint texture;
texture = SOIL_load_OGL_texture(("resources/textures/" + fileName + ".png").c_str(),
   SOIL_LOAD_AUTO, // 问题出在这里
   SOIL_CREATE_NEW_ID,
   SOIL_FLAG_INVERT_Y | SOIL_FLAG_MULTIPLY_ALPHA | SOIL_FLAG_NTSC_SAFE_RGB);

glBindTexture(GL_TEXTURE_2D, texture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glBindTexture(GL_TEXTURE_2D, NULL);

解决方案：改用stb_image加载 #

最终放弃SOIL2，改用stb_image加载纹理，通过配置GL_TEXTURE_SWIZZLE参数并手动实现SOIL_FLAG_MULTIPLY_ALPHA的逻辑，解决了灰度纹理显示问题。

新的纹理加载代码 #

void Texture::create() noexcept {
    if (hasLogger()) logger->info("Loading «" + fileName + "» texture...");

    if (isCreated()) {
        if (hasLogger()) logger->warn("Attempt to create texture «" + fileName + "» that is already created");
        return;
    }

    int width, height, nrChannels;
    stbi_set_flip_vertically_on_load(true); // 翻转Y轴以适配OpenGL坐标系
    stbi_uc* data = stbi_load(("resources/textures/" + fileName + ".png").c_str(), &width, &height, &nrChannels, 0);

    if (data) {
        GLuint texture;

        glGenTextures(1, &texture);
        glBindTexture(GL_TEXTURE_2D, texture);

        GLenum format;
        switch (nrChannels) {
            case 1: { // 单通道灰度图
                format = GL_RED;
                // 配置纹理通道重映射，将R通道复制到G、B通道，A通道设为1
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_R, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_G, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_B, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_A, GL_ONE);
                break;
            }
            case 2: { // 灰度+Alpha通道
                format = GL_RG;
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_R, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_G, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_B, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_A, GL_GREEN);

                // 实现SOIL_FLAG_MULTIPLY_ALPHA的逻辑：灰度值乘以Alpha值
                for (int i = 0; i < 2 * width * height; i += 2) {
                    data[i] = (data[i] * data[i + 1] + 128) >> 8;
                }

                break;
            }
            case 3: default: { // RGB三通道
                format = GL_RGB;
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_R, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_G, GL_GREEN);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_B, GL_BLUE);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_A, GL_ONE);
                break;
            }
            case 4: { // RGBA四通道
                format = GL_RGBA;
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_R, GL_RED);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_G, GL_GREEN);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_B, GL_BLUE);
                glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_SWIZZLE_A, GL_ALPHA);

                // 实现SOIL_FLAG_MULTIPLY_ALPHA的逻辑：RGB值乘以Alpha值
                for (int i = 0; i < 4 * width * height; i += 4) {
                    data[i + 0] = (data[i + 0] * data[i + 3] + 128) >> 8;
                    data[i + 1] = (data[i + 1] * data[i + 3] + 128) >> 8;
                    data[i + 2] = (data[i + 2] * data[i + 3] + 128) >> 8;
                }

                break;
            }
        }

        // 根据纹理格式设置环绕方式，带Alpha的纹理使用边缘钳位
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, format == GL_RGBA || format == GL_RG ? GL_CLAMP_TO_EDGE : GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, format == GL_RGBA || format == GL_RG ? GL_CLAMP_TO_EDGE : GL_REPEAT);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
        glBindTexture(GL_TEXTURE_2D, NULL);

        stbi_image_free(data);

        this->texture = texture;
        created = true;
    }
    else {
        if (hasLogger()) logger->fatal("Failed to create texture «" + fileName + "»");
    }
}

内容的提问来源于stack exchange，提问作者Unable error