CODEWITHSUNDEEP
c++libpng
Brandon
Brandon

Reputation: 23498

LibPng Read Into Struct

I cannot seem to get libpng to dump its data into my struct. I can't figure out what I'm doing wrong. I'm trying to flip the bytes because PNG's are stored top->down and I need the data bottom->up.

First my struct looks like:

typedef union RGB
{
    uint32_t Color;
    struct
    {
        unsigned char B, G, R, A;
    } RGBA;
} *PRGB;

Then I created a vector as such:

png_init_io(PngPointer, hFile);
png_set_sig_bytes(PngPointer, 8);
png_read_info(PngPointer, InfoPointer);

uint32_t width, height;
int bitdepth, colortype, interlacetype, channels;

png_set_strip_16(PngPointer);
channels = png_get_channels(PngPointer, InfoPointer);
png_get_IHDR(PngPointer, InfoPointer, &width, &height, &bitdepth, &colortype, &interlacetype, nullptr, nullptr);


uint32_t RowBytes = png_get_rowbytes(PngPointer, InfoPointer);
unsigned char** RowPointers = png_get_rows(PngPointer, InfoPointer);
std::vector<RGB> Pixels(RowBytes * height);   //Amount of bytes in one row * height of image.

//Crashes in the for loop below :S

for (int I = 0; I < height; I++)
{
    for (int J = 0; J < width; J++)
    {
        Pixels[(height - 1 - I) * width + J].RGBA.B = *(RowPointers[J]++);
        Pixels[(height - 1 - I) * width + J].RGBA.G = *(RowPointers[J]++);
        Pixels[(height - 1 - I) * width + J].RGBA.R = *(RowPointers[J]++);
    }
}

std::fclose(hFile);
png_destroy_read_struct(&PngPointer, &InfoPointer, nullptr);

What did I do wrong? How can I get the pixels of the PNG and store them upside down? I used the same technique for bitmaps but PNG just isn't working :l

Upvotes: 1

Views: 538

Answers (1)

JasonD
JasonD

Reputation: 16582

Shouldn't this:

Pixels[(height - 1 - I) * width + J].RGBA.B = *(RowPointers[J]++);

Index RowPointers via I instead?

Upvotes: 3

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