add build script for nixos support

Makefile

@@ -1,4 +1,3 @@
-CC = clang
 CFLAGS = -Wall -Wextra -std=c99 -pedantic -O2
 LIBS = -lSDL2 -lm
 

build.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+source /etc/os-release
+
+# Don't know how to just have SDL2 available on NixOS
+if echo $ID | grep "nixos" 2>/dev/null >/dev/null; then
+    nix-shell -p SDL2 --run make
+else
+    make
+fi

main.c

@@ -372,6 +372,8 @@ main(void)
         uint32_t buttons = SDL_GetMouseState(NULL, NULL);
         if (buttons & SDL_BUTTON(3))
             break;
+        else if (buttons & SDL_BUTTON(1))
+            screenshot(state.canvas);
 
         clear_canvas(state.canvas, BLACK);