diff --git a/analogue.c b/analogue.c
index c06f5d7..45a29f2 100644
--- a/analogue.c
+++ b/analogue.c
@@ -32,7 +32,7 @@ int main(int argc, char** argv)
 	res = SDL_Init(SDL_INIT_VIDEO | SDL_INIT_GAMECONTROLLER);
 	if (res < 0)
 		goto error;
-	
+
 	const int winpos = SDL_WINDOWPOS_CENTERED;
 	const int winflg = SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
 	int winw = WINDOW_WIDTH;
@@ -44,16 +44,13 @@ int main(int argc, char** argv)
 		goto error;
 	}
 
-	const int rendflags = SDL_RENDERER_PRESENTVSYNC;
-	rend = SDL_CreateRenderer(window, -1, rendflags);
-	if (rend == NULL)
+	if (InitDraw(window))
 	{
 		res = -1;
 		goto error;
 	}
 
-	int rw, rh;
-	SDL_GetRendererOutputSize(rend, &rw, &rh);
+	rect rendRect = GetDrawSizeInPixels();
 
 	if ((res = SDL_GameControllerAddMappingsFromFile("gamecontrollerdb.txt")) != -1)
 		printf("read %d mappings from gamecontrollerdb.txt\n", res);
@@ -130,7 +127,7 @@ int main(int argc, char** argv)
 					{
 						winw = event.window.data1;
 						winh = event.window.data2;
-						SDL_GetRendererOutputSize(rend, &rw, &rh);
+						rendRect = GetDrawSizeInPixels();
 						repaint = true;
 					}
 					else if (event.window.event == SDL_WINDOWEVENT_EXPOSED)
@@ -224,23 +221,23 @@ int main(int argc, char** argv)
 			}
 			while (SDL_PollEvent(&event) > 0);
 		}
-		
+
 		if (repaint)
 		{
 			// background
 			SetDrawColour(0x1F1F1FFF);
 			DrawClear();
 
-			const int hrw = rw / 2;
-			DrawDigital(&(rect){0, 0, hrw, rh}, &stickl);
-			DrawAnalogue(&(rect){hrw, 0, hrw, rh}, &stickr);
+			const int hrw = rendRect.w / 2;
+			DrawDigital(&(rect){0, 0, hrw, rendRect.h}, &stickl);
+			DrawAnalogue(&(rect){hrw, 0, hrw, rendRect.h}, &stickr);
 
 			// test player thingo
 			if (showavatar)
 			{
 				plrpos = VecAdd(plrpos, VecScale(stickl.compos, framedelta * 0.5));
-				plrpos.x = pfmod(plrpos.x, rw);
-				plrpos.y = pfmod(plrpos.y, rh);
+				plrpos.x = pfmod(plrpos.x, rendRect.w);
+				plrpos.y = pfmod(plrpos.y, rendRect.h);
 
 				SetDrawColour(0xFF0000FF);
 				const int plrSz = 32;
@@ -250,15 +247,15 @@ int main(int argc, char** argv)
 					plrSz, plrSz);
 			}
 
-			SDL_RenderPresent(rend);
+			DrawPresent();
 			repaint = false;
 		}
 	}
-	
+
 	res = 0;
 error:
 	SDL_GameControllerClose(pad);
-	SDL_DestroyRenderer(rend);
+	QuitDraw();
 	SDL_DestroyWindow(window);
 	SDL_Quit();
 	return res;
diff --git a/draw.c b/draw.c
index 21cdf4d..45fd736 100644
--- a/draw.c
+++ b/draw.c
@@ -2,7 +2,29 @@
 #include "maths.h"
 #include <SDL_render.h>
 
-SDL_Renderer* rend = NULL;
+static SDL_Renderer* rend = NULL;
+
+int InitDraw(SDL_Window* window)
+{
+	const int rendflags = SDL_RENDERER_PRESENTVSYNC;
+	rend = SDL_CreateRenderer(window, -1, rendflags);
+	return (rend == NULL) ? -1 : 0;
+}
+
+void QuitDraw(void)
+{
+	SDL_DestroyRenderer(rend);
+	rend = NULL;
+}
+
+
+rect GetDrawSizeInPixels(void)
+{
+	rect out = {0, 0, 0, 0};
+	SDL_GetRendererOutputSize(rend, &out.w, &out.h);
+	return out;
+}
+
 
 void SetDrawColour(uint32_t c)
 {
@@ -60,3 +82,8 @@ void DrawCircleSteps(int x, int y, int r, int steps)
 		lasty = ofsy;
 	}
 }
+
+void DrawPresent(void)
+{
+	SDL_RenderPresent(rend);
+}
diff --git a/draw.h b/draw.h
index 51fab08..56160c4 100644
--- a/draw.h
+++ b/draw.h
@@ -3,17 +3,64 @@
 
 #define DISPLAY_SCALE 0.8889
 
+#include "maths.h"
 #include <stdint.h>
 
-typedef struct SDL_Renderer SDL_Renderer;
-extern SDL_Renderer* rend;
+typedef struct SDL_Window SDL_Window;
 
+// Initialise the drawing subsystem.
+//
+// Params:
+//   window - The application's SDL window.
+//
+// Returns:
+//   0 on success, -1 on failure.
+int InitDraw(SDL_Window* window);
+
+// Quit the drawing subsystem.
+//
+// This is safe (but pointless) to call when the drawing
+// subsystem is uninitialised.
+void QuitDraw(void);
+
+// Get the actual size of the canvas in pixels.
+//
+// Returns:
+//   rectangle struct with 'w' and 'h' set to the width &
+//   height of the canvas in actual pixels.
+rect GetDrawSizeInPixels(void);
+
+// Set the current draw colour.
+//
+// Params:
+//   c - Colour in the unsigned 32-bit int packed format of:
+//       0xFF000000 - red channel
+//       0x00FF0000 - blue channel
+//       0x0000FF00 - green channel
+//       0x000000FF - alpha channel
 void SetDrawColour(uint32_t c);
+
+// Clear the entire screen using the current draw colour.
 void DrawClear(void);
+
+// Draw a single pixel point at x, y w/ the draw colour.
 void DrawPoint(int x, int y);
+
+// Draw rectangle outline.
 void DrawRect(int x, int y, int w, int h);
+
+// Draw straight line between x1,y1 and x2,y2.
 void DrawLine(int x1, int y1, int x2, int y2);
+
+// Draw outline circle.
 void DrawCircle(int x, int y, int r);
+
+// Draw outline circle made of lines w/ a discrete number of steps.
+//
+// Can be used to draw regular convex polygons such as an octagon.
 void DrawCircleSteps(int x, int y, int r, int steps);
 
+// Present the current buffer to the screen.
+void DrawPresent(void);
+
 #endif//DRAW_H