glTexImage2D切片和对齐问题出现在窗口中 [英] glTexImage2D slicing and alignment issues appearing in window

问题描述

我正在制作自己的地形图，并且我一直在使用NASA的.hgt文件.

I'm working on making my own topographic map, and I have been using .hgt files from NASA.

我正在使用加载文件

void MapImage::load_map_file(const char* filename) {
    std::ifstream file(filename, std::ios::in | std::ios::binary);
    if (!file) {
        std::cout << "Error opening file!" << std::endl;
    }
    std::vector<short> tempHeight(TOTAL_SIZE);
    unsigned char buffer[2];

    int x, y;
    for (int i = 0; i < TOTAL_SIZE; i++) {
        if (!file.read(reinterpret_cast<char*>(buffer), sizeof(buffer))) {
            std::cout << "Error reading file!" << std::endl;
        }
        tempHeight[i] = (buffer[0] << 8) | buffer[1];
    }

    height = tempHeight;
}

然后使用以下命令将它们添加到内存位图中:

And then adding them to an inmemory bitmap using:

void MapImage::loadTextureImage() {
img_tex = 0;
glGenTextures(1, &img_tex);

int x, y, w, h;
w = h = SRTM_SIZE;
unsigned char* img;
img = (unsigned char *)malloc(3 * w * h);
memset(img, 0, sizeof(img));

int g = 0;
double height_color;

/*
for(int i = 0; i < TOTAL_SIZE; i++){
    height_color = (float)height[i] / 10.0;
    g = (height_color * 255);
    if (g>255)g = 255;

    img[i * 3 + 2] = (unsigned char)0;
    img[i * 3 + 1] = (unsigned char)g;
    img[i * 3 + 0]= (unsigned char)0;
}
*/

for (int i = 0; i < w; i++) {
    for (int j = 0; j < h; ++j) {
        x = i; 
        y = (h - 1) - j;

        height_color = (float)height[j + (i * w)] / 10.0;
        g = (height_color * 255);
        if (g>255)g = 255;

        img[(x + y*w) * 3 + 2] = (unsigned char)0;
        img[(x + y*w) * 3 + 1] = (unsigned char)g;
        img[(x + y*w) * 3]     = (unsigned char)0;
    }
}


glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, img_tex);

glTexImage2D(
    GL_TEXTURE_2D,
    0,
    GL_RGB,
    w,
    h,
    0,
    GL_RGB,
    GL_UNSIGNED_BYTE,
    img
);
}

但是，这样会导致图像被切成角，像这样

However this results in a image with the corner sliced, like this

在loadTextureImage()中使用注释的版本看起来略有不同，但是切片了相同的角.

Using the commented version in the loadTextureImage() looks slightly different, however with the same corner sliced.

有人暗示发生了什么吗?我尝试将图像用作纹理，并加载到stbi库中，并且效果很好，所以我不确定哪里出了问题.

Does anyone have a hint to whats going on? I've tried using a image as a texture, loading with the stbi library, and that works fine, so I'm not sure where it's going wrong.

(图像坐标为N10E099)

(the coordinates for the image is N10E099)

推荐答案

这看起来像是行对齐错误，由3宽度的颜色数据引起.尝试在 glTexImage2D 之前使用以下调用:

This looks like row misalignment, caused by the 3-wide colour data. Try using the following call just before glTexImage2D:

glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

每当读取纹理数据发送到GPU时， glTexImage2D 及其朋友都会使用此对齐值，默认情况下为 4 .

This alignment value, which is 4 by default, is used by glTexImage2D and friends whenever texture data is read to be sent to the GPU.

无法验证它与数据的实际外观是否匹配，因此在像您这样的情况下，某行未在4字节边界处结束，下一行的前几个字节将被跳过，从而导致这种对角线变形.

There is no verification that it matches what the data actually looks like, so in cases like yours where a row doesn't end on a 4-byte boundary, the first few bytes of the next row will be skipped, leading to this diagonal distortion.

另一个方向(从GPU到客户端内存)的纹理数据传输通过 glPixelStorei(GL_PACK_ALIGNMENT，1); 进行对齐.

Texture data transfers in the other direction (from the GPU to client memory) are aligned via glPixelStorei(GL_PACK_ALIGNMENT, 1);.

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