From 8d062a90b1ffbe9e00334fa3e9e939406bd32141 Mon Sep 17 00:00:00 2001
From: Nathan Reiner <nathan@nathanreiner.xyz>
Date: Sun, 2 Feb 2025 16:00:15 +0100
Subject: screen: add vsync and double buffering

---
 src/screen/main.zig | 86 +++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 67 insertions(+), 19 deletions(-)

(limited to 'src/screen/main.zig')

diff --git a/src/screen/main.zig b/src/screen/main.zig
index 1a33fd0..f11f628 100644
--- a/src/screen/main.zig
+++ b/src/screen/main.zig
@@ -1,5 +1,6 @@
 const std = @import("std");
 const drm = @import("drm/card.zig");
+const Event = @import("drm/event.zig").Event;
 
 pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
@@ -38,35 +39,82 @@ pub fn main() !void {
 
     std.debug.print("crtc = {}\n", .{ crtc.id });
 
-    var framebuffer = try card.create_frame_buffer(mode.horizontal.size, mode.vertical.size, 32);
-    defer framebuffer.deinit();
+    var double_buffer = try card.create_double_buffer(mode.horizontal.size, mode.vertical.size, 32);
+    defer double_buffer.deinit();
 
-    std.debug.print("framebuffer = {}, {}\n", .{ framebuffer.id, framebuffer.canvas_size });
+    std.debug.print("buffer = {}, {}x{}, stride = {}\n", .{
+        double_buffer.buffer().id,
+        double_buffer.buffer().width,
+        double_buffer.buffer().height,
+        double_buffer.buffer().stride,
+    });
 
-    try crtc.attach(&framebuffer, &connector, mode);
+    try crtc.attach(double_buffer.crtc_buffer(), &connector, mode);
 
-    var frame: u24 = 0;
+    const Pos = struct { x: f32, y: f32 };
+
+    var vec = Pos { .x = 10, .y = 10 };
+    var pos = Pos { .x = 0, .y = 0 };
+    var delta: f32 = 0;
+    const size = 100;
+
+    const width: f32 = @floatFromInt(double_buffer.buffer().width);
+    const height: f32 = @floatFromInt(double_buffer.buffer().height);
 
     while (true) {
-        for (0..framebuffer.width) |x| {
-            for (0..framebuffer.height) |y| {
-                const raster_x = (frame + x) / 100 * 100;
-                const raster_y = y / 100 * 100;
-                const color = ((raster_x + raster_y) + 0x129453) * 0x329120;
-                framebuffer.set(@intCast(x), @intCast(y), .{
-                    .red = @intCast(color & 0xff),
-                    .green = @intCast((color >> 8) & 0xff),
-                    .blue = @intCast((color >> 16) & 0xff),
+        const start = try std.time.Instant.now();
+
+        double_buffer.buffer().fill(.{ .red = 0, .green = 0, .blue = 0 });
+
+        pos.x += vec.x * delta;
+        pos.y += vec.y * delta;
+
+        if (pos.x < 0) {
+            pos.x = -pos.x;
+            vec.x = -vec.x;
+        } else if (pos.x + size >= width) {
+            pos.x = width - size;
+            vec.x = -vec.x;
+        }
+
+        if (pos.y < 0) {
+            pos.y = -pos.y;
+            vec.y = -vec.y;
+        } else if (pos.y + size >= height) {
+            pos.y = height - size;
+            vec.y = -vec.y;
+        }
+
+        for (0..size) |w| {
+            for (0..size) |h| {
+                double_buffer.buffer().set(
+                    @as(u32, @intFromFloat(pos.x)) + @as(u32, @intCast(w)),
+                    @as(u32, @intFromFloat(pos.y)) + @as(u32, @intCast(h)),
+                    .{
+                    .red = 0xff,
+                    .green = 0,
+                    .blue = 0,
                 });
             }
         }
 
-        frame, _ = @addWithOverflow(frame, 1);
+        const end = try std.time.Instant.now();
+        const elapsed = (@as(f32, @floatFromInt(end.since(start))) / std.time.ns_per_s);
+        std.debug.print("FPS: {d:.2}\r", .{ 1 / elapsed });
+        delta = elapsed * 60;
 
-        try crtc.attach(&framebuffer, &connector, mode);
+        try crtc.page_flip(&double_buffer);
 
-        std.time.sleep(@intFromFloat(1000000000 / mode.frame_rate()));
-    }
+        while (true) {
+            var event: ?Event = null;
+            while (event == null) {
+                event = try card.poll_event(5000);
+            }
 
-    while (true) { std.time.sleep(5000000000); }
+            switch ((event orelse unreachable).type) {
+                .page_flip_complete => break,
+                else => {},
+            }
+        }
+    }
 }
-- 
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