module main

import gg
import rand

const max_circles_per_pass = 1000

// prepare some random colors ahead of time
const colors = []gg.Color{len: max_circles_per_pass, init: gg.Color{
    r: u8(index * 0 + rand.u8())
    g: u8(index * 0 + rand.u8())
    b: u8(index * 0 + rand.u8())
}}

fn frame(mut ctx gg.Context) {
    // First pass, just clears the background:
    ctx.begin()
    ctx.end()

    // We want to draw thousands of circles, but sokol has a limit for how
    // many primitives can be in a single pass, and if you reach that limit
    // you will not see *anything at all* for that pass.
    // For the circles below, that limit is ~2520 circles per pass.
    // To overcome this, we will use several passes instead, where each one
    // will draw just 1000 circles.
    // In other words, in total we will have 4 * 1000 = 4000 circles, drawn with
    // 4 passes.
    for i := 0; i < 4 * max_circles_per_pass; i += max_circles_per_pass {
        ctx.begin()
        for c in 0 .. max_circles_per_pass {
            rx := rand.int_in_range(0, ctx.window.width) or { 0 }
            ry := rand.int_in_range(0, ctx.window.height) or { 0 }
            ctx.draw_circle_filled(rx, ry, 10, colors[c])
        }
        ctx.end(how: .passthru)
    }

    // The last pass, is for the fps overlay, that should be *always on top of everything*.
    // Drawing it in a separate pass, guarantees, that it *will* be drawn, even if the drawing
    // of all the other passes fail. Try increasing max_circles_per_pass to 3000 for example.
    ctx.begin()
    ctx.show_fps()
    ctx.end(how: .passthru)
}

fn main() {
    mut ctx := gg.new_context(
        window_title: 'Many Thousands of Circles'
        bg_color:     gg.black
        width:        600
        height:       400
        frame_fn:     frame
    )
    ctx.run()
}