#include <c64.h>
#include <stdint.h>

// Memory locations for C64 bitmap mode
#define BITMAP_MEM ((uint8_t*)0x2000)

// Safe integer absolute value
int iabs(int v) {
    return v < 0 ? -v : v;
}

// Project a 3D point to 2D using simple perspective projection
void project(int x, int y, int z, int *sx, int *sy) {
    int distance = 4;
    int scale = 60;
    int px = x * scale / (z + distance);
    int py = y * scale / (z + distance);

    *sx = px + 160;  // Center on screen (320x200)
    *sy = py + 100;
}

// Draw a pixel into the hi-res bitmap
void set_pixel(uint8_t *bitmap, int x, int y) {
    if (x < 0 || x >= 320 || y < 0 || y >= 200) return;

    int offset = (y * 320 + x);
    int byte_index = offset / 8;
    int bit = 7 - (x % 8);
    bitmap[byte_index] |= (1 << bit);
}

// Bresenham line draw
void draw_line(uint8_t *bitmap, int x0, int y0, int x1, int y1) {
    int dx = iabs(x1 - x0), sx = x0 < x1 ? 1 : -1;
    int dy = -iabs(y1 - y0), sy = y0 < y1 ? 1 : -1;
    int err = dx + dy, e2;

    while (1) {
        set_pixel(bitmap, x0, y0);
        if (x0 == x1 && y0 == y1) break;
        e2 = 2 * err;
        if (e2 >= dy) { err += dy; x0 += sx; }
        if (e2 <= dx) { err += dx; y0 += sy; }
    }
}

void main(void) {
    uint8_t *bitmap = BITMAP_MEM;

    // Enable bitmap mode
    VIC.ctrl1 |= 0x20;  // Set bit 5 to enable bitmap
    VIC.addr = (VIC.addr & 0xF1) | 0x08; // Bitmap at $2000, screen at $0400

    // Clear bitmap manually (8000 bytes)
    for (int i = 0; i < 8000; i++) {
        bitmap[i] = 0x00;
    }

    // Cube 3D coordinates
    int cube[8][3] = {
        {-1, -1, -1}, { 1, -1, -1}, { 1,  1, -1}, {-1,  1, -1},
        {-1, -1,  1}, { 1, -1,  1}, { 1,  1,  1}, {-1,  1,  1}
    };

    // Projected 2D coordinates
    int proj[8][2];

    // Project all 3D points to 2D screen coords
    for (int i = 0; i < 8; i++) {
        project(cube[i][0], cube[i][1], cube[i][2], &proj[i][0], &proj[i][1]);
    }

    // Draw cube edges (12 total)
    const uint8_t edges[12][2] = {
        {0,1}, {1,2}, {2,3}, {3,0},
        {4,5}, {5,6}, {6,7}, {7,4},
        {0,4}, {1,5}, {2,6}, {3,7}
    };

    for (int i = 0; i < 12; i++) {
        draw_line(bitmap,
                  proj[edges[i][0]][0], proj[edges[i][0]][1],
                  proj[edges[i][1]][0], proj[edges[i][1]][1]);
    }

    // Stay alive
    while (1) { }
}