From d9e09a9cbe6f9225a2bc827ec3df60385b22c361 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <rekai@musuka.dev>
Date: Tue, 23 May 2023 02:24:11 -0500
Subject: [PATCH] fix(ui): remove flickering on ui pause/timeout

---
 src/imgui.zig    | 13 +++++++++----
 src/platform.zig | 22 ++++++++++++----------
 2 files changed, 21 insertions(+), 14 deletions(-)

diff --git a/src/imgui.zig b/src/imgui.zig
index 337d7b3..bb58b42 100644
--- a/src/imgui.zig
+++ b/src/imgui.zig
@@ -12,6 +12,7 @@ const emu = @import("core/emu.zig");
 const Gui = @import("platform.zig").Gui;
 const Arm7tdmi = @import("core/cpu.zig").Arm7tdmi;
 const RingBuffer = @import("zba-util").RingBuffer;
+const Dimensions = @import("platform.zig").Dimensions;
 
 const Allocator = std.mem.Allocator;
 const GLuint = gl.GLuint;
@@ -66,8 +67,10 @@ pub const State = struct {
     }
 };
 
-pub fn draw(state: *State, tex_id: GLuint, cpu: *Arm7tdmi) void {
-    const win_scale = config.config().host.win_scale;
+pub fn draw(state: *State, win_dim: Dimensions, tex_id: GLuint, cpu: *Arm7tdmi) bool {
+    const scn_scale = config.config().host.win_scale;
+
+    zgui.backend.newFrame(@intToFloat(f32, win_dim.width), @intToFloat(f32, win_dim.height));
 
     {
         _ = zgui.beginMainMenuBar();
@@ -142,8 +145,8 @@ pub fn draw(state: *State, tex_id: GLuint, cpu: *Arm7tdmi) void {
     }
 
     {
-        const w = @intToFloat(f32, gba_width * win_scale);
-        const h = @intToFloat(f32, gba_height * win_scale);
+        const w = @intToFloat(f32, gba_width * scn_scale);
+        const h = @intToFloat(f32, gba_height * scn_scale);
 
         const window_title = std.mem.sliceTo(&state.title, 0);
         _ = zgui.begin(window_title, .{ .flags = .{ .no_resize = true, .always_auto_resize = true } });
@@ -318,6 +321,8 @@ pub fn draw(state: *State, tex_id: GLuint, cpu: *Arm7tdmi) void {
     {
         zgui.showDemoWindow(null);
     }
+
+    return true; // request redraw
 }
 
 const widgets = struct {
diff --git a/src/platform.zig b/src/platform.zig
index d5f3b25..5922768 100644
--- a/src/platform.zig
+++ b/src/platform.zig
@@ -21,7 +21,7 @@ const GLsizei = gl.GLsizei;
 const SDL_GLContext = *anyopaque;
 const Allocator = std.mem.Allocator;
 
-const Dimensions = struct { width: u32, height: u32 };
+pub const Dimensions = struct { width: u32, height: u32 };
 const default_dim: Dimensions = .{ .width = 1280, .height = 720 };
 
 pub const sample_rate = 1 << 15;
@@ -187,7 +187,7 @@ pub const Gui = struct {
                 }
             }
 
-            zgui.backend.newFrame(@intToFloat(f32, win_dim.width), @intToFloat(f32, win_dim.height));
+            var zgui_redraw: bool = false;
 
             switch (self.state.emulation) {
                 .Transition => |inner| switch (inner) {
@@ -249,18 +249,20 @@ pub const Gui = struct {
                         opengl_impl.drawScreenTexture(emu_tex, prog_id, objects, buf);
                     }
 
-                    imgui.draw(&self.state, out_tex, cpu);
+                    zgui_redraw = imgui.draw(&self.state, win_dim, out_tex, cpu);
                 },
-                .Inactive => imgui.draw(&self.state, out_tex, cpu),
+                .Inactive => zgui_redraw = imgui.draw(&self.state, win_dim, out_tex, cpu),
             }
 
-            // Background Colour
-            const size = zgui.io.getDisplaySize();
-            gl.viewport(0, 0, @floatToInt(GLsizei, size[0]), @floatToInt(GLsizei, size[1]));
-            gl.clearColor(0, 0, 0, 1.0);
-            gl.clear(gl.COLOR_BUFFER_BIT);
+            if (zgui_redraw) {
+                // Background Colour
+                const size = zgui.io.getDisplaySize();
+                gl.viewport(0, 0, @floatToInt(GLsizei, size[0]), @floatToInt(GLsizei, size[1]));
+                gl.clearColor(0, 0, 0, 1.0);
+                gl.clear(gl.COLOR_BUFFER_BIT);
 
-            zgui.backend.draw();
+                zgui.backend.draw();
+            }
 
             SDL.SDL_GL_SwapWindow(self.window);
         }