我正在尝试使用 SDL2 为波前对象的 OpenGL 渲染加载纹理(目前我正在使用固定管道进行测试，但我最终计划转移到着色器)。问题是应用于四边形的加载纹理(以及使用纹理右下角的一小部分的模型)看起来像这样:

_{(来源:image-upload.de)}

This is the texture I used

当使用 SDL 函数绘制时，图像加载正常并且看起来完全正常，因此可能是转换为 OGL 纹理时出现问题。请注意，我启用了 alpha 混合并且纹理仍然完全不透明 - 因此值不是完全随机的，并且可能不是未初始化的内存。 这是我用于转换表面的代码(从此处网站上的各种教程和问题拼凑而成):

GLuint glMakeTexture(bool mipmap = false, int request_size = 0) { // Only works on 32 Bit Surfaces
    GLuint texture = 0;
    if ((bool)_surface) {
        int w,h;
        if (request_size) { // NPOT and rectangular textures are widely supported since at least a decade now; you should never need this...
            w = h = request_size;
            if (w<_surface->w || h<_surface->h) return 0; // No can do.
        } else {
            w = _surface->w;
            h = _surface->h;
        }

        SDL_LockSurface(&*_surface);
        std::cout<<"Bits: "<<(int)_surface->format->BytesPerPixel<<std::endl;

        Uint8 *temp = (Uint8*)malloc(w*h*sizeof(Uint32)); // Yes, I know it's 4...
        if (!temp) return 0;

        // Optimized code
        /*for (int y = 0; y<h; y++) { // Pitch is given in bytes, so we need to cast to 8 bit here!
            memcpy(temp+y*w*sizeof(Uint32),(Uint8*)_surface->pixels+y*_surface->pitch,_surface->w*sizeof(Uint32));
            if (w>_surface->w) memset(temp+y*w*sizeof(Uint32)+_surface->w,0,(w-_surface->w)*sizeof(Uint32));
        }
        for (int y = _surface->h; y<h; y++) memset(temp+y*w*sizeof(Uint32),0,w*sizeof(Uint32));
        GLenum format = (_surface->format->Rmask==0xFF)?GL_RGBA:GL_BGRA;*/

        // Naive code for testing
        for (int y = 0; y<_surface->h; y++)
            for (int x = 0; x<_surface->w; x++) {
                int mempos = (x+y*w)*4;
                SDL_Color pcol = get_pixel(x,y);
                temp[mempos] = pcol.r;
                temp[mempos+1] = pcol.g;
                temp[mempos+2] = pcol.b;
                temp[mempos+3] = pcol.a;
            }
        GLenum format = GL_RGBA;

        SDL_UnlockSurface(&*_surface);

        glGenTextures(1, &texture);
        glBindTexture(GL_TEXTURE_2D, texture);
        if (mipmap) glTexParameteri(texture, GL_GENERATE_MIPMAP, GL_TRUE);
        glTexImage2D(GL_TEXTURE_2D, 0, format, w, h, 0, format, GL_UNSIGNED_BYTE, temp);
        if (mipmap) glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        else glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        free(temp); // Always clean up...
    }
    return texture;
}

编辑:_surface 实际上是 SDL_Surface 的 std::shared_ptr。因此， &* 当(解锁)锁定它时。

顺便说一句，SDL 声称表面在我的机器上被格式化为 32 位 RGBA，我已经检查过了。

绑定(bind)纹理和绘制四边形的代码在这里:

glEnable(GL_TEXTURE_2D);
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glBindTexture(GL_TEXTURE_2D,_texture[MAP_KD]);

static bool once = true;
if (once) {
    int tex;
    glGetIntegerv(GL_TEXTURE_BINDING_2D, &tex);
    bool valid = glIsTexture(tex);
    std::cout<<tex<<" "<<valid<<std::endl;
    once = false;
}
glBegin(GL_TRIANGLE_STRIP);
    //glColor3f(1.f,1.f,1.f);
    glNormal3f(0,1,0);
    glTexCoord2f(0.f,0.f); glVertex3f(0,0,0);
    glTexCoord2f(0.f,1.f); glVertex3f(0,0,1);
    glTexCoord2f(1.f,0.f); glVertex3f(1,0,0);
    glTexCoord2f(1.f,1.f); glVertex3f(1,0,1);
glEnd();

斧头是稍后从索引列表中绘制的；代码太长，无法在此处共享(此外，除了纹理外，它工作正常)。

我还尝试了在许多教程中找到的将 _surface->pixels 传递给 glTexImage2D() 的天真方法，但这也无济于事(而且我听说这样做是错误的方法，因为 pitch!=width*一般为 BytesPerPixel)。 注释掉的“优化”代码看起来完全一样，顺便说一句(正如预期的那样)。我写了下半部分是为了更好的测试。将所有像素设置为特定颜色或使纹理部分透明会按预期工作，因此我假设 OpenGL 正确加载了 temp 中的值。这可能是我对 SDL2 Surfaces 中内存布局的理解搞砸了。

最终编辑:解决方案(重置 GL_UNPACK_ROW_LENGTH 是关键，感谢 Peter Clark):

GLuint glTexture(bool mipmap = false) {
    GLuint texture = 0;
    if ((bool)_surface) {
        GLenum texture_format, internal_format, tex_type;
        if (_surface->format->BytesPerPixel == 4) {
            if (_surface->format->Rmask == 0x000000ff) {
                texture_format = GL_RGBA;
                tex_type = GL_UNSIGNED_INT_8_8_8_8_REV;
            } else {
                texture_format = GL_BGRA;
                tex_type = GL_UNSIGNED_INT_8_8_8_8;
            }
            internal_format = GL_RGBA8;
        } else {
            if (_surface->format->Rmask == 0x000000ff) {
                texture_format = GL_RGB;
                tex_type = GL_UNSIGNED_BYTE;
            } else {
                texture_format = GL_BGR;
                tex_type = GL_UNSIGNED_BYTE;
            }
            internal_format = GL_RGB8;
        }

        int alignment = 8;
        while (_surface->pitch%alignment) alignment>>=1; // x%1==0 for any x
        glPixelStorei(GL_UNPACK_ALIGNMENT,alignment);

        int expected_pitch = (_surface->w*_surface->format->BytesPerPixel+alignment-1)/alignment*alignment;
        if (_surface->pitch-expected_pitch>=alignment) // Alignment alone wont't solve it now
            glPixelStorei(GL_UNPACK_ROW_LENGTH,_surface->pitch/_surface->format->BytesPerPixel);
        else glPixelStorei(GL_UNPACK_ROW_LENGTH,0);

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

        glTexImage2D(GL_TEXTURE_2D, 0, internal_format, _surface->w, _surface->h, 0, texture_format, tex_type, _surface->pixels);
        if (mipmap) {
            glGenerateMipmap(GL_TEXTURE_2D);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        } else {
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        }
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        glPixelStorei(GL_UNPACK_ALIGNMENT,4);
        glPixelStorei(GL_UNPACK_ROW_LENGTH,0);
    }
    return texture;
}

最佳答案

像素存储对齐

您需要告诉 OpenGL 图像的对齐方式是 glPixelStorei(GL_UNPACK_ALIGNMENT, [1,2,4,8]) .这将是 2 的最大幂，它是最大 8 的除数。如果它不是可接受的值之一，您可能必须另外设置 GL_UNPACK_ROW_LENGTH - 参见 this answer for more details and advice on that topic .需要注意的一件事 - GL_UNPACK_ROW_LENGTH 是行长度以像素为单位，而 SDL_Surface::pitch 是行长度以字节为单位。最重要的是，您必须确保 internal_format、format 和 pixel_type 设置为与 SDL_Surface 包含的内容相匹配。 One more resource on this topic.

“完整”纹理

// Load texture into surface...
// Error check..
// Bind GL texture...

// Calculate required align using pitch (largest power of 2 that is a divisor of pitch)

glPixelStorei(GL_UNPACK_ALIGNMENT, align);
//glPixelStorei(GL_UNPACK_ROW_LENGTH, row_length); // row_length = pitch / bytes_per_pixel

glTexImage2D(
  GL_TEXTURE_2D, 
  0, 
  internal_format,
  sdl_surface->w,
  sdl_surface->h,
  0, 
  format,
  pixel_type, 
  sdl_surface->pixels);
// Check for errors

if(use_mipmaps)
{
  glGenerateMipmap(GL_TEXTURE_2D);
  // Check for errors

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, /* filter mode */);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, /* filter mode */);
  // Check for errors
}
else
{
  // This makes the texture complete 
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);

  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, /* filter mode */);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, /* filter mode */);
  // Check for errors
}

// Potentially reset GL_UNPACK_ALIGNMENT and/or GL_UNPACK_ROW_LENGTH to their default values
// Cleanup

#ifdef MYPROJ_GRAPHICS_DEBUG
#define ASSERT_IF_GL_ERROR \
{ \
  GLenum last_error = glGetError(); \
  if(last_error != GL_NO_ERROR); \
  { \
    printf("GL Error: %d", last_error); \
  } \
  __debugbreak(); // Visual Studio intrinsic - other compilers have similar intrinsics
} 
#else
#define ASSERT_IF_GL_ERROR
#endif

关于c++ - 从 SDL2 表面创建 OpenGL 纹理 - 奇怪的像素值，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25771735/