blur.cpp

#include <cstdio>
#include <iostream>
#include <cairo.h>

using namespace std;

struct RGBA {
    int a, r, g, b;
};
const int bytes_per_row = 4;
const int BLUR = 20;

RGBA read_pixel(int w, int h, unsigned char* data, int x, int y) {
    RGBA ret;
    int stride = bytes_per_row * w;
    int a_loc = stride * y + x * bytes_per_row + 0,
        r_loc = stride * y + x * bytes_per_row + 1,
        g_loc = stride * y + x * bytes_per_row + 2,
        b_loc = stride * y + x * bytes_per_row + 3;

    ret.a = data[a_loc];
    ret.r = data[r_loc];
    ret.g = data[g_loc];
    ret.b = data[b_loc];

    return ret;
}

void write_pixel(int w, int h, unsigned char* data, int x, int y, RGBA pixel) {
    int stride = bytes_per_row * w;
    int a_loc = stride * y + x * bytes_per_row + 0,
        r_loc = stride * y + x * bytes_per_row + 1,
        g_loc = stride * y + x * bytes_per_row + 2,
        b_loc = stride * y + x * bytes_per_row + 3;

    data[a_loc] = pixel.a;
    data[r_loc] = pixel.r;
    data[g_loc] = pixel.g;
    data[b_loc] = pixel.b;
}

void add_pixel(RGBA &dest, RGBA src) {
    dest.a += src.a;
    dest.r += src.r;
    dest.g += src.g;
    dest.b += src.b;
}

void scale_pixel(RGBA &pixel, float lambda) {
    pixel.a *= lambda;
    pixel.r *= lambda;
    pixel.g *= lambda;
    pixel.b *= lambda;
}

int main() {
    cairo_surface_t* source_surface = cairo_image_surface_create_from_png("dionyziz.png");
    cairo_format_t source_fmt = cairo_image_surface_get_format(source_surface);
    int w = cairo_image_surface_get_width(source_surface);
    int h = cairo_image_surface_get_height(source_surface);
    int stride = cairo_image_surface_get_stride(source_surface);
    int bytes_per_row = stride / w;
    unsigned char* source_data = cairo_image_surface_get_data(source_surface);
    unsigned char* dest_data = (unsigned char*)malloc(stride * h);
    int i = 0;

    for (int y = 0; y < h; ++y) {
        for (int x = 0; x < w; ++x) {
            RGBA pixel = (RGBA){0, 0, 0, 0};

            int cnt = 0;
            for (int dx = -BLUR; dx <= BLUR; ++dx) {
                for (int dy = -BLUR; dy <= BLUR; ++dy) {
                    if (x + dx >= 0 && x + dx < w && y + dy >= 0 && y + dy < h) {
                        RGBA neighbour_pixel = read_pixel(w, h, source_data, x + dx, y + dy);

                        add_pixel(pixel, neighbour_pixel);
                        ++cnt;
                    }
                }
            }
            scale_pixel(pixel, 1.0 / cnt);
            write_pixel(w, h, dest_data, x, y, pixel);
        }
    }
    cout << "Blurred image " << w << "x" << h << " with stride " << stride << endl;

    cairo_surface_t* dest_surface = cairo_image_surface_create_for_data(dest_data, source_fmt, w, h, stride);
    cairo_surface_write_to_png(dest_surface, "dionyziz-blurred.png");

    return 0;
}