problems loading a bitmap

[szhou42]

I am using vbe, mode 0x118 (1024*768*24)
This is a 1024*768*24 bitmap(The link is jpg, but I convert it to bitmap before loading it)


After loading this bitmap into my os, it looks like this



So, weird black horizontal lines and dotted lines coming from no where...

Filling the screen with one color works fine, anyone knows what's wrong with it ?

[alexfru]

Memory corruption? Using memory after freeing (including using automatic/local arrays after going out of the function scope where they're defined)?

[BrightLight]

alexfru made it there before me; I was just going to say that it's most likely memory corruption.
EDIT: Notice that the BMP image inside your OS is horizontally inverted; if you'd like BMP parsing code, I have a function for that (only works on 24-bit BMP images, but can easily be extended.)

[Ch4ozz]

Looks like your stack is inside the buffer.
Find out if the picture buffer itself was corrupted or if its the vram

[szhou42]

Looks like your stack is inside the buffer.
Find out if the picture buffer itself was corrupted or if its the vram

alexfru made it there before me; I was just going to say that it's most likely memory corruption.
EDIT: Notice that the BMP image inside your OS is horizontally inverted; if you'd like BMP parsing code, I have a function for that (only works on 24-bit BMP images, but can easily be extended.)

Memory corruption? Using memory after freeing (including using automatic/local arrays after going out of the function scope where they're defined)?

Hi, I think it's not due to memory corruption of the picture buffer, because it's allocated by a heap allocator and does not overlap with the stack, and I never free the heap.

Also, I compared the vram and the picture immediately after the picture buffer was copied to the vram, they're not the same.
(since the actual picture pixels in bmp file are reversed, I've to copy them in the reversed direction)

Code: Select all

void weird_memcpy(void * dest, void * src, uint32_t count) {
    char * p1 = dest, * p2 = src;;
    while(count-- > 0) {
        memcpy(p1, p2-3, 3);
        p1 = p1 + 3;
        p2 = p2 - 3;
    }
}
void bitmap_display(bitmap_t * bmp) {
    if(!bmp) return;
    void * data = bmp->image_bytes;
    char * image = data;
    char * screen = (char*)0xfc000000;
    weird_memcpy(screen, data + bmp->width * bmp->height * 3, bmp->width * bmp->height);

    // Compare the video ram and the data
    uint32_t count = bmp->width * bmp->height * 3;
    char * p1 = screen, * p2 = image + bmp->width * bmp->height * 3;
    while(count-- > 0) {
        char first = *(p2-3);
        char second = *(p2-2);
        char third = *(p2-1);
        if(first != *p1)
            printf("no no no\n");
        if(second != *(p1+1))
            printf("no no no\n");
        if(third != *(p1+2))
            printf("no no no\n");
        p1 = p1 + 3;
        p2 = p2 - 3;
    }
    printf("yeah yeah yeah\n");
}

[Kazinsal]

The pixels in a BMP are still left-to right, but the rows are stored bottom to top -- the packed pixels are not completely reversed.

[szhou42]

The pixels in a BMP are still left-to right, but the rows are stored bottom to top -- the packed pixels are not completely reversed.

Ohoh I couldn't believe I didn't notice that. but this doesn't explain the black horizontal lines I guess

[szhou42]

I've found the bug, it's in my filesystem, thank you guys!

[szhou42]

Fixed