c - 在 OpenGL 中渲染每面具有不同纹理的立方体

Question

我使用 Sprite 表，然后使用立方体侧面、顶部和底部的纹理坐标创建三个数组。我的问题是，无论出于何种原因，我的 block 的每一面都是使用 tex_bottom 数组中的纹理绘制的。

这是加载纹理的函数:

int load_gl_texture(const char *filename, unsigned char *image, unsigned width, unsigned height) {
    int status = 0;

    while(!lodepng_decode32_file(&image, &width, &height, filename)) {
        GLint texSize;
        glGetIntegerv(GL_MAX_TEXTURE_SIZE, &texSize);

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

        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, width, height, 0, GL_RGBA,
            GL_UNSIGNED_BYTE, image);

        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
        glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);

        status = 1;
        break;
    }
    if (image)
        free(image);

    return status;

}

这是绘制立方体的代码:

    glBegin(GL_QUADS);

    // Front Face
    glTexCoord2fv(tex_sides[0]); glVertex3fv(vertices[1]);  // Bottom Left Of The Texture and Quad
    glTexCoord2fv(tex_sides[1]); glVertex3fv(vertices[0]);  // Bottom Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[2]); glVertex3fv(vertices[4]);  // Top Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[3]); glVertex3fv(vertices[5]);  // Top Left Of The Texture and Quad

    // Back Face
    glTexCoord2fv(tex_sides[1]); glVertex3fv(vertices[2]);  // Bottom Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[2]); glVertex3fv(vertices[6]);  // Top Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[3]); glVertex3fv( vertices[7]);  // Top Left Of The Texture and Quad
    glTexCoord2fv(tex_sides[0]); glVertex3fv( vertices[3]);  // Bottom Left Of The Texture and Quad

    // Top Face
    glTexCoord2fv(tex_top[3]); glVertex3fv(vertices[7]);  // Top Left Of The Texture and Quad
    glTexCoord2fv(tex_top[0]); glVertex3fv(vertices[5]);  // Bottom Left Of The Texture and Quad
    glTexCoord2fv(tex_top[1]); glVertex3fv( vertices[4]);  // Bottom Right Of The Texture and Quad
    glTexCoord2fv(tex_top[2]); glVertex3fv( vertices[6]);  // Top Right Of The Texture and Quad

    // Bottom Face
    glTexCoord2fv(tex_bottom[2]); glVertex3fv(vertices[0]);  // Top Right Of The Texture and Quad
    glTexCoord2fv(tex_bottom[3]); glVertex3fv( vertices[2]);  // Top Left Of The Texture and Quad
    glTexCoord2fv(tex_bottom[0]); glVertex3fv( vertices[3]);  // Bottom Left Of The Texture and Quad
    glTexCoord2fv(tex_bottom[1]); glVertex3fv(vertices[1]);  // Bottom Right Of The Texture and Quad

    // Right face
    glTexCoord2fv(tex_sides[1]); glVertex3fv( vertices[2]);  // Bottom Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[2]); glVertex3fv( vertices[6]);  // Top Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[3]); glVertex3fv( vertices[4]);  // Top Left Of The Texture and Quad
    glTexCoord2fv(tex_sides[0]); glVertex3fv( vertices[0]);  // Bottom Left Of The Texture and Quad

    // Left Face
    glTexCoord2fv(tex_sides[0]); glVertex3fv(vertices[3]);  // Bottom Left Of The Texture and Quad
    glTexCoord2fv(tex_sides[1]); glVertex3fv(vertices[1]);  // Bottom Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[2]); glVertex3fv(vertices[5]);  // Top Right Of The Texture and Quad
    glTexCoord2fv(tex_sides[3]); glVertex3fv(vertices[7]);  // Top Left Of The Texture and Quad

    glEnd();

是什么导致了这个问题以及如何解决它？

Answer 1

我发现了问题所在。我将 block ID 转换为纹理坐标的函数存在缺陷，因为它返回了函数内部使用的内存地址，而不是返回实际值。一旦没有变量保存相应的内存地址，这就会导致这些值被垃圾收集。为了解决这个问题，我做了以下更改:

旧:

float* block_id_to_coordinates(int id) {
    GLfloat tex = {(id % 16)/16.0, (id / 16)/16.0};
    return tex;
} 

新:

void block_id_to_coordinates(int id, GLfloat tex[]) {
    tex[0] = (id % 16)/16.0;
    tex[1] = (id / 16)/16.0;
} 

新函数改为使用在draw_block函数中声明的变量，以便它们可以在整个绘图过程中使用。所以像这样:

float type_top[2];
block_id_to_coordinates(top, type_top); // Initialize array using the "constructor" function

float type_sides[2];
block_id_to_coordinates(sides, type_sides);

float type_bottom[2];
block_id_to_coordinates(bottom, type_bottom);