alpha_test.psh

// Alpha Blending Test for blit_bgra32()

let WIDTH = 800;
let HEIGHT = 600;

// Helper to create a 32-bit BGRA color value
fun bgra32(r, g, b, a) {
    return (a << 24) | (r << 16) | (g << 8) | b;
}

// Helper function to draw a filled rectangle
fun draw_rect(buffer, xmin, ymin, w, h, color) {
    let x_start = (0).max(xmin);
    let y_start = (0).max(ymin);
    let x_end = WIDTH.min(xmin + w);
    let y_end = HEIGHT.min(ymin + h);
    let clipped_width = x_end - x_start;
    if (clipped_width <= 0) return;

    for (let var j = y_start; j < y_end; ++j) {
        let start_index = j * WIDTH + x_start;
        buffer.fill_u32(start_index, clipped_width, color);
    }
}

// --- 1. Create a checkerboard background ---
let bg_buf = ByteArray.with_size(WIDTH * HEIGHT * 4);
let TILE_SIZE = 20;
for (let var j = 0; j < (HEIGHT / TILE_SIZE).ceil(); ++j) {
    for (let var i = 0; i < (WIDTH / TILE_SIZE).ceil(); ++i) {
        let color = ((i + j) % 2 == 0) ? bgra32(100, 100, 100, 255) : bgra32(150, 150, 150, 255);
        draw_rect(bg_buf, i * TILE_SIZE, j * TILE_SIZE, TILE_SIZE, TILE_SIZE, color);
    }
}

// --- 2. Create a foreground surface with an alpha gradient ---
let FG_WIDTH = 400;
let FG_HEIGHT = 400;
let fg_buf = ByteArray.with_size(FG_WIDTH * FG_HEIGHT * 4);

for (let var j = 0; j < FG_HEIGHT; ++j) {
    for (let var i = 0; i < FG_WIDTH; ++i) {
        // Horizontal gradient from transparent to opaque red
        let alpha = (i * 255 / FG_WIDTH).floor();
        let color = bgra32(255, 30, 30, alpha);
        fg_buf.set_u32(j * FG_WIDTH + i, color);
    }
}

// --- 3. Blit the foreground onto the background ---
// The user mentioned this is a method on ByteArray
// The arguments are: dst_width, dst_height, src_buf, src_width, src_height, dst_x, dst_y
bg_buf.blit_bgra32(
    WIDTH, HEIGHT,
    fg_buf, FG_WIDTH, FG_HEIGHT,
    ((WIDTH - FG_WIDTH) / 2).floor(), ((HEIGHT - FG_HEIGHT) / 2).floor()
);

/*
// --- 4. Performance Test ---
let NUM_BLITS = 1000;
let start_time = $time_current_ms();
for (let var i = 0; i < NUM_BLITS; ++i) {
    bg_buf.blit_bgra32(
        WIDTH, HEIGHT,
        fg_buf, FG_WIDTH, FG_HEIGHT,
        ((WIDTH - FG_WIDTH) / 2).floor(), ((HEIGHT - FG_HEIGHT) / 2).floor()
    );
}
let end_time = $time_current_ms();
let total_time = end_time - start_time;
let avg_time = total_time / NUM_BLITS;
$println("Blit performance test:");
$println("Total time for " + NUM_BLITS.to_s() + " blits: " + total_time.to_s() + " ms");
$println("Average time per blit: " + avg_time.to_s() + " ms");
*/

// --- 5. Create a window and draw the result ---
let window = $window_create(WIDTH, HEIGHT, "Alpha Blending Test", 0);
$window_draw_frame(window, bg_buf);

// --- 5. Event Loop ---
loop {
    let msg = $actor_recv();
    if (msg instanceof UIEvent && (msg.kind == 'CLOSE_WINDOW' || (msg.kind == 'KEY_DOWN' && msg.key == 'ESCAPE'))) {
        break;
    }
}