纹理不会出现 FreeGLUT

Question

我有一个带照明的简单平面（方形）和 material，我想在上面放一个地球纹理。但什么也没有出现。我检查过，认为它正确加载了 RGB 数据，所以我猜测这条线有问题（数据是 *char，图像是 BMP24）

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, outWidth, outHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid*)data);

这里是一个 .bmp 加载函数：

GLuint LoadTexture(const char* imagepath) {
    printf("Reading image %s\n", imagepath);
    unsigned int outWidth = -1;
    unsigned int outHeight = -1;
    unsigned char header[54];
    unsigned int dataPos;
    unsigned int imageSize;

    FILE* file;
    if (errno_t err = fopen_s(&file, imagepath, "rb") != 0) {
        perror("Can't Open file");
        return 0;
    }

    // If less than 54 byes are read, problem
    if (fread(header, 1, 54, file) != 54) {
        printf("Not a correct BMP file\n");
        return NULL;
    }
    // A BMP files always begins with "BM"
    if (header[0] != 'B' || header[1] != 'M') {
        printf("Not a correct BMP file\n");
        return NULL;
    }
    // Make sure this is a 24bpp file
    if (*(int*)&(header[0x1E]) != 0) { printf("Not a correct BMP file\n");    return NULL; }
    if (*(int*)&(header[0x1C]) != 24) { printf("Not a correct BMP file\n");    return NULL; }

    // Read the information about the image
    dataPos = *(int*)&(header[0x0A]);
    outWidth = *(int*)&(header[0x12]);
    outHeight = *(int*)&(header[0x16]);
    imageSize = *(int*)&(header[0x22]);

    // Some BMP files are misformatted, guess missing information
    if (imageSize == 0)    imageSize = outWidth * outHeight * 3; // 3 : one byte for each Red, Green and Blue component
    if (dataPos == 0)      dataPos = 54; // The BMP header is done that way

    // Read the actual data from the file into the buffer
    unsigned char* data = new unsigned char[imageSize];
    fread(data, 3, imageSize, file);


    // Everything is in memory now, the file wan be closed
    fclose(file);

    GLuint tex;
    glGenTextures(1, &tex);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, outWidth, outHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid*)data);

    return tex;
}

这里是主要和显示功能：

void render(void) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    float ratio = 0.75;
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, earthTextureData);

    glBegin(GL_QUADS);
    glVertex3f(-0.5, -0.5, 0);
    glVertex3f(-0.5, 0.5, 0);
    glVertex3f(0.5, 0.5, 0);
    glVertex3f(0.5, -0.5, 0);
    glEnd();

    glDisable(GL_TEXTURE_2D);

    glutSwapBuffers();
}


int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(1200, 800);
    glutCreateWindow("app");

    init(); // custome initilizing
    initLighting();

    earthTextureData = LoadTexture("Texture/globe.bmp");

    glutDisplayFunc(render);
    glutReshapeFunc(reshape);
    glutMotionFunc(mouseMove);
    glutKeyboardFunc(keyboard);
    glutIdleFunc(idle);

    glutMainLoop();
}

我试过代码，有时（当我使用 int 而不是 char* 时）我得到一个红色 material 覆盖所有内容但不知道到底是什么原因造成的

更新：必须更改几行才能使其正常工作（对于 bmp24 文件）：

1-编辑此行： fread(数据, 1, imageSize, 文件);

2- 添加这一行： glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);

3- 编辑这一行（为了正确显示颜色）： glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, outWidth, outHeight, 0, GL_BGR_EXT, GL_UNSIGNED_BYTE, (GLvoid*)data);

4-添加UV坐标（查找glTexCoord）

Answer 1

您必须将 UV 坐标告知 OpenGL，以了解放置该纹理的位置和方式。这可以在您的渲染函数中完成。

UV 坐标范围为 0.0 - 1.0，并告诉 OpenGL 如何将纹理放置到渲染器上。

Here is a good picture that illustrates uv coordinates well

像这样的东西应该可以工作：

void render(void) {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    float ratio = 0.75;
    glEnable(GL_TEXTURE_2D);
    glBindTexture(GL_TEXTURE_2D, earthTextureData);

    glBegin(GL_QUADS);
    glTexCoord3f(0.0, 0.0, 0.0);
    glVertex3f(-0.5, -0.5, 0);

    glTexCoord3f(0.0, 1.0, 0.0);
    glVertex3f(-0.5, 0.5, 0);

    glTexCoord3f(1.0, 1.0, 0.0);
    glVertex3f(0.5, 0.5, 0);

    glTexCoord3f(1.0, 0.0, 0);
    glVertex3f(0.5, -0.5, 0);
    glEnd();

    glDisable(GL_TEXTURE_2D);

    glutSwapBuffers();
}

Answer 2

您错过了通过 glTexParameter 设置纹理参数的设置。

如果不生成mipmaps (by glGenerateMipmap)，那么设置GL_TEXTURE_MIN_FILTER很重要。由于默认过滤器是 GL_NEAREST_MIPMAP_LINEAR 如果您不将缩小功能更改为 GL_NEAREST 或 GL_LINEAR.

，纹理将是不完整的 mipmap

当图像加载到纹理对象时，GL_UNPACK_ALIGNMENT 必须设置为 1。
默认情况下 GL_UNPACK_ALIGNMENT 为 4，因此假定图像的每一行对齐到 4 个字节。一个BMP文件的像素一般都是3个字节大小，而且是紧密排列的，这样会造成错位。

GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, outWidth, outHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, (GLvoid*)data);
glPixelStorei(GL_UNPACK_ALIGNMENT, 4);

当然你必须通过 glTexCoord, before specifying the vertex coordinate (glVertex) 设置纹理参数，如另一个答案中所述：

glBindTexture(GL_TEXTURE_2D, earthTextureData);

glEnable(GL_TEXTURE_2D);
glBegin(GL_QUADS);

glTexCoord2f(0.0, 0.0);
glVertex3f(-0.5, -0.5, 0);

glTexCoord2f(0.0, 1.0);
glVertex3f(-0.5, 0.5, 0);

glTexCoord2f(1.0, 1.0);
glVertex3f(0.5, 0.5, 0);

glTexCoord2f(1.0, 0.0);
glVertex3f(0.5, -0.5, 0);

glEnd();
glDisable(GL_TEXTURE_2D);

纹理不会出现 FreeGLUT

Texture wont appear FreeGLUT

c++

opengl

glut

texture-mapping

freeglut