From dccf7bf421ca62ec8f1c470be4aa72d60dd7201d Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Mon, 13 Apr 2020 09:52:16 +0200
Subject: More usable

---
 window.h | 61 ++++++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 42 insertions(+), 19 deletions(-)

diff --git a/window.h b/window.h
index d9ac9d9..5d67a9a 100644
--- a/window.h
+++ b/window.h
@@ -60,14 +60,19 @@ public:
 		std::vector<uint8_t> &arr;
 	};
 
-	/// The draw buffer will be of size 3 * width * height; row-major order, RGB pixels.
+	enum Action {
+		ACT_REDRAW,
+		ACT_STOP,
+		ACT_OK,
+	};
+
+	/// The draw buffer will be of size 3 * width * height; row-major order,
+	/// RGB pixels. The draw handler will be invoked if the event handler
+	/// returns ACT_REDRAW, but also possibly in other circumstances (e.g.
+	/// window resize).
 	using DrawHandler = std::function<void(Buffer &buffer)>;
-	/// Return true to stop the event loop.
-	using EventHandler = std::function<bool(const SDL_Event&)>;
+	using EventHandler = std::function<Action(const SDL_Event&)>;
 
-	/// The draw function will be called after each invocation of the event
-	/// function, and might also be invoked more often as the user re-focuses the
-	/// window.
 	inline void event_loop(EventHandler eventfunc, DrawHandler drawfunc);
 
 private:
@@ -124,7 +129,23 @@ inline void Window::event_loop(EventHandler eventfunc, DrawHandler drawfunc) {
 
 		if (e.type == SDL_QUIT) break;
 
-		if (eventfunc(e)) break;
+		bool need_redraw = false;
+		bool need_refresh = false;
+
+		if (e.type == SDL_WINDOWEVENT) {
+			if (e.window.event == SDL_WINDOWEVENT_FOCUS_GAINED) {
+				need_refresh = true;
+			}
+		}
+
+		Action act = eventfunc(e);
+		switch (act) {
+			case ACT_STOP: return;
+			case ACT_REDRAW: need_redraw = true; break;
+			case ACT_OK: break;
+			default:
+				throw std::logic_error("Invalid Action from EventHandler");
+		}
 
 		int width, height;
 		SDL_GetWindowSize(win, &width, &height);
@@ -139,19 +160,22 @@ inline void Window::event_loop(EventHandler eventfunc, DrawHandler drawfunc) {
 				drawbuf.data(), surf_wid, surf_hei, 24, 3 * surf_wid,
 				255, 255 << 8, 255 << 16, 0
 			);
+			need_redraw = true;
 		}
 
-		{
+		if (need_redraw) {
 			Buffer buffer{width, height, drawbuf};
 			drawfunc(buffer);
 		}
 
-		SDL_Surface *winsurf = SDL_GetWindowSurface(win);
-		if (SDL_MUSTLOCK(winsurf)) SDL_LockSurface(winsurf);
-		SDL_BlitSurface(surface, nullptr, winsurf, nullptr);
-		if (SDL_MUSTLOCK(winsurf)) SDL_UnlockSurface(winsurf);
+		if (need_redraw || need_refresh) {
+			SDL_Surface *winsurf = SDL_GetWindowSurface(win);
+			if (SDL_MUSTLOCK(winsurf)) SDL_LockSurface(winsurf);
+			SDL_BlitSurface(surface, nullptr, winsurf, nullptr);
+			if (SDL_MUSTLOCK(winsurf)) SDL_UnlockSurface(winsurf);
 
-		SDL_UpdateWindowSurface(win);
+			SDL_UpdateWindowSurface(win);
+		}
 	}
 }
 
@@ -180,10 +204,9 @@ inline void Window::Buffer::plot(int x, int y, Clr clr, float alpha) {
 
 inline void Window::Buffer::plotf(float x, float y, Clr clr, float alpha) {
 	const int x0 = x, y0 = y;
-	const float xal = (x - x0) * alpha;
-	const float yal = (y - y0) * alpha;
-	plot(x0    , y0    , clr, (1 - xal) * (1 - yal));
-	plot(x0 + 1, y0    , clr, xal       * (1 - yal));
-	plot(x0    , y0 + 1, clr, (1 - xal) * yal      );
-	plot(x0 + 1, y0 + 1, clr, xal       * yal      );
+	const float xal = x - x0, yal = y - y0;
+	plot(x0    , y0    , clr, (1 - xal) * (1 - yal) * alpha);
+	plot(x0 + 1, y0    , clr, xal       * (1 - yal) * alpha);
+	plot(x0    , y0 + 1, clr, (1 - xal) * yal       * alpha);
+	plot(x0 + 1, y0 + 1, clr, xal       * yal       * alpha);
 }
-- 
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