Time scaling with the Spell key

app.c

@@ -29,6 +29,7 @@ App *app_NewApp() {
 	app->time     = gametime_NewSystem(app);
 
 	app->switch_level = NULL;
+	app->timescale    = 1.0;
 	app->clear_color  = 0;
 	app->wantQuit     = false;
 	app->paused       = false;
@@ -71,6 +72,9 @@ void app_Advance(App *app, Duration deltaTime) {
 
 	input_Advance(app->input);
 
+	if (1.0 - app->timescale > EPS)
+		deltaTime.microseconds = deltaTime.microseconds * app->timescale;
+
 	if (!app->paused) {
 		gametime_Advance(app->time, deltaTime);
 		particle_Advance(app->particle, deltaTime);

app.h

@@ -27,6 +27,7 @@ typedef struct _App {
 	System_GameTime *time;
 
 	char    *switch_level;
+	double   timescale;
 	uint32_t clear_color;
 	bool     wantQuit, debugOn;
 	bool     paused;

app_render.cpp

@@ -12,6 +12,7 @@
 #include "render_util.h"
 #include "util/vector.h"
 #include <math.h>
+#include <stdio.h>
 #include <graphics.h>
 
 
@@ -178,5 +179,11 @@ void app_Render(App *app) {
 		RECT rect = {.left = SCREEN_WIDTH / 2 - 10, .top = 100, .right = SCREEN_WIDTH / 2 + 10, .bottom = 200};
 		drawtext("Game Paused", &rect, DT_CENTER | DT_NOCLIP);
 	}
+	if (abs(app->timescale - 1.0) > EPS) {
+		RECT rect = {.left = SCREEN_WIDTH / 2 - 10, .top = 50, .right = SCREEN_WIDTH / 2 + 10, .bottom = 150};
+		char buf[128];
+		snprintf(buf, sizeof(buf), "*** TIMESCALE %.2lf ***", app->timescale);
+		drawtext(buf, &rect, DT_CENTER | DT_NOCLIP);
+	}
 }
 }

input.c

@@ -64,6 +64,12 @@ void input_Advance(System_Input *sys) {
 		}
 	}
 
+	if (input_IsPressed(sys->keys[input_Key_Spell])) {
+		sys->super->timescale = 0.25;
+	} else {
+		sys->super->timescale = 1.0;
+	}
+
 	if (sys->keys[input_Key_Escape] == JustPressed) {
 		if (!sys->super->paused)
 			fprintf(stderr, "[input_Advance] Pausing\n");