diff --git a/Makefile b/Makefile
index 3826d3e..1b40d7c 100644
--- a/Makefile
+++ b/Makefile
@@ -1,12 +1,17 @@
 all : glslview glslwrite
 
-USE_INOTIFY = -DUSE_INOTIFY
+ifeq ($(shell uname -s),Linux)
+USE_INOTIFY ?= -DUSE_INOTIFY
+endif
 
-CFLAGS = -O3 -Wall $(USE_INOTIFY)
-LIBS = -lSDL2 -lGL -lGLEW -lm
+CFLAGS ?= -O3 -Wall
+LIBS := -lSDL2 -lGL -lGLEW -lm
 
 glslview : glslview.c common.c common.h
-	$(CC) $(CFLAGS) -o $@ glslview.c common.c $(LIBS)
+	$(CC) $(CFLAGS) $(USE_INOTIFY) -o $@ glslview.c common.c $(LIBS)
 
 glslwrite : glslwrite.c common.c common.h
 	$(CC) $(CFLAGS) -o $@ glslwrite.c common.c $(LIBS) -lpng
+
+clean :
+	rm -f glslview glslwrite
diff --git a/README.txt b/README.txt
new file mode 100644
index 0000000..f329dec
--- /dev/null
+++ b/README.txt
@@ -0,0 +1,129 @@
+glslview
+========
+
+glslview is a simple program to run GLSL fragment shaders and interact with them.
+
+glslview will render a simple fullscreen rectangle, the shader will determine each
+pixel's color.
+
+The glslwrite tool can be used to write the generated frames to PNG files
+(with transparency support!).
+
+You will need a graphics adapter and drivers with modern OpenGL/GLSL support.
+
+Building
+~~~~~~~~
+
+glslview has been tested on Linux only, but it should work on other systems as well.
+If it doesn't, I'm happy to take patches.
+
+glslview has the following dependencies:
+
+* SDL2
+* libGL
+* libGLEW
+
+glslwrite additionally depends on libpng.
+
+On Linux, glslview will use inotify to watch the loaded shader file for changes.
+
+
+Running
+~~~~~~~
+
+Shader
+------
+
+glslview will supply the following uniform parameters to the shader:
+
+vec2 res
+    The current resolution of the window
+
+float time
+    Current time in milliseconds (by default since start of the program)
+
+int param0, param1, param2
+    Modifiable parameters, 0 by default
+
+The shader must define an output vec4 called "fragColor" into which the fragment color
+is to be written.
+
+See the examples provided with the source for more information. The "symmetry"
+example makes use of all parameters.
+
+
+Command line
+------------
+
+    glslview <options> <shader>
+    glslwrite <options> <shader> <output directory>
+
+
+Common options:
+
+-w <width>
+    Initial window width (default: 800)
+
+-h <height>
+    Initial window height (default: 800)
+
+-0, -1, -2 <param>
+    Initial value for the shader parameters
+
+
+glslview options:
+
+-s <speed>
+    Initial speed factor (default: 1.0, negative values make time run backwards)
+
+-t <time>
+    Initial time value (default: 0.0)
+
+
+glslwrite options:
+
+-s <step>
+    Time step between frames (default: 20.0)
+
+-f <frame>
+    Number of frames to generate (default: run forever)
+
+
+glslview control
+----------------
+
++/-, scroll wheel
+    Change speed
+
+=
+    Reset speed
+
+<
+    Run backwards
+
+>
+    Run forwards
+
+r
+    Reset time
+
+R
+    Reset parameters
+
+l
+    Reload shader (if you're using a system without inotify, or inotify fails)
+
+Space
+    Pause/continue
+
+Page up/down
+    Modify param0
+
+Left/right
+    Modify param1
+
+Up/down
+    Modify param2
+
+Escape
+    Quit
diff --git a/common.c b/common.c
index e9258c1..b459f31 100644
--- a/common.c
+++ b/common.c
@@ -36,9 +36,9 @@
 char *filename;
 float current_time = 0;
 
-GLint param0 = 0;
-GLint param1 = 0;
-GLint param2 = 0;
+int param0 = 0;
+int param1 = 0;
+int param2 = 0;
 
 
 static GLint time_loc;
diff --git a/common.h b/common.h
index 7cbf34d..8f45105 100644
--- a/common.h
+++ b/common.h
@@ -25,18 +25,13 @@
 
 #pragma once
 
-#include <GL/glew.h>
-
-#include <SDL2/SDL.h>
-#include <SDL2/SDL_opengl.h>
-
 
 extern char *filename;
 extern float current_time;
 
-extern GLint param0;
-extern GLint param1;
-extern GLint param2;
+extern int param0;
+extern int param1;
+extern int param2;
 
 
 void load(void);
diff --git a/examples/checkers.frag b/examples/checkers.frag
index 77de622..2e42704 100644
--- a/examples/checkers.frag
+++ b/examples/checkers.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/polygon.frag b/examples/polygon.frag
index a018865..26b3b10 100644
--- a/examples/polygon.frag
+++ b/examples/polygon.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/snail.frag b/examples/snail.frag
index 5513d34..079bd63 100644
--- a/examples/snail.frag
+++ b/examples/snail.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/square-in-circle.frag b/examples/square-in-circle.frag
index 731eca6..4207bbb 100644
--- a/examples/square-in-circle.frag
+++ b/examples/square-in-circle.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/square-in-square.frag b/examples/square-in-square.frag
index 07343d8..13ef58d 100644
--- a/examples/square-in-square.frag
+++ b/examples/square-in-square.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/square-ring.frag b/examples/square-ring.frag
index 300d4ef..0779981 100644
--- a/examples/square-ring.frag
+++ b/examples/square-ring.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/square-ring2.frag b/examples/square-ring2.frag
index 26310a7..19da887 100644
--- a/examples/square-ring2.frag
+++ b/examples/square-ring2.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/squares.frag b/examples/squares.frag
index 574f220..353da2d 100644
--- a/examples/squares.frag
+++ b/examples/squares.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/supersnail.frag b/examples/supersnail.frag
index dd0f77c..724b264 100644
--- a/examples/supersnail.frag
+++ b/examples/supersnail.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/examples/symmetry.frag b/examples/symmetry.frag
index 26f4651..363c18a 100644
--- a/examples/symmetry.frag
+++ b/examples/symmetry.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
@@ -56,13 +56,13 @@ void main(void) {
 	float k = param1;
 
 	for (int i = 0; i < n; i++) {
-		mat3 t = scale(0.3 + 0.02 * param2)
-		       * rot(-PI/2*(k*i/n + time/1500))
-		       * trans(0.5, 0.0)
-		       * rot(2*PI*i/n)
-		       * scale(1 / (1 + 0.03 * param2));
+		mat3 t = scale(1 + 0.03 * param2)
+		       * rot(-2*PI*i/n)
+		       * trans(-0.5, 0.0)
+		       * rot(PI/2*(k*i/n + time/1500))
+		       * scale(1 / (0.3 + 0.02 * param2));
 
-		float c = square(p * inverse(t));
+		float c = square(p * t);
 		scene = abs(scene - c);
 	}
 
diff --git a/examples/torus.frag b/examples/torus.frag
index 06f6987..bf99ecb 100644
--- a/examples/torus.frag
+++ b/examples/torus.frag
@@ -1,4 +1,4 @@
-#version 330
+#version 130
 
 out vec4 fragColor;
 
diff --git a/glslview.c b/glslview.c
index 42c9e93..2444725 100644
--- a/glslview.c
+++ b/glslview.c
@@ -25,14 +25,20 @@
 
 #include "common.h"
 
-
+#include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
 #include <math.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 
+#include <GL/glew.h>
+
+#include <SDL2/SDL.h>
+#include <SDL2/SDL_opengl.h>
+
 #ifdef USE_INOTIFY
 # include <sys/inotify.h>
 # include <sys/stat.h>
@@ -40,6 +46,13 @@
 #endif
 
 
+static int init_param0 = 0;
+static int init_param1 = 0;
+static int init_param2 = 0;
+static float init_time = 0;
+static float init_speed = 1.0;
+
+static bool paused = false;
 static float speed = 1.0;
 static unsigned previous_ticks = 0;
 
@@ -53,22 +66,20 @@ static int inotify_watch = -1;
 static void reset_watch(void) {
 	if (inotify_watch >= 0) {
 		if (inotify_rm_watch(inotify_fd, inotify_watch)) {
-			fprintf(stderr, "unable to remove watch\n");
+			fprintf(stderr, "unable to remove watch: %s\n", strerror(errno));
 			exit(1);
 		}
 	}
 
 	inotify_watch = inotify_add_watch(inotify_fd, filename, IN_CLOSE_WRITE);
-	if (inotify_watch < 0) {
-		fprintf(stderr, "unable to watch '%s' for changes\n", filename);
-		return;
-	}
+	if (inotify_watch < 0)
+		fprintf(stderr, "unable to watch '%s' for changes: %s\n", filename, strerror(errno));
 }
 
 static void init_watch(void) {
 	inotify_fd = inotify_init();
 	if (inotify_fd < 0) {
-		fprintf(stderr, "unable to initialize inotify\n");
+		fprintf(stderr, "unable to initialize inotify: %s\n", strerror(errno));
 		exit(1);
 	}
 
@@ -94,9 +105,20 @@ static void check_reload(void) {}
 
 static void update(void) {
 	unsigned ticks = SDL_GetTicks();
-	current_time += speed * (ticks - previous_ticks);
-	previous_ticks = ticks;
 
+	if (!paused)
+		current_time += speed * (ticks - previous_ticks);
+
+	previous_ticks = ticks;
+}
+
+static void set_speed(float v) {
+	speed = v;
+	printf("speed: %f\n", v);
+}
+
+static void print_params(void) {
+	printf("params: %i %i %i\n", (int)param0, (int)param1, (int)param2);
 }
 
 static void handle_input(const char *input) {
@@ -108,46 +130,99 @@ static void handle_input(const char *input) {
 			break;
 
 		case 'r':
-			current_time = 0;
+			current_time = init_time;
 			break;
 
 		case 'R':
-			param0 = param1 = param2 = 0;
+			param0 = init_param0;
+			param1 = init_param1;
+			param2 = init_param2;
+			print_params();
 			break;
 
 		case '+':
-			speed *= 1.1;
+			set_speed(speed * 1.1);
 			break;
 
 		case '-':
-			speed /= 1.1;
+			set_speed(speed / 1.1);
 			break;
 
 		case '=':
 			if (speed < 0)
-				speed = -1.0;
+				set_speed(-init_speed);
 			else
-				speed = 1.0;
+				set_speed(init_speed);
 			break;
 
 		case '<':
 			if (speed > 0)
-				speed = -speed;
+				set_speed(-speed);
 			break;
 
 		case '>':
 			if (speed < 0)
-				speed = -speed;
+				set_speed(-speed);
+			break;
+
+		case ' ':
+			paused = !paused;
 		}
 	}
 }
 
+static void usage(void) {
+	fprintf(stderr, "Usage: glslview [-w <width>] [-h <height>] [-t <time>] [-s <speed>] [-0 <param0>] [-1 <param1>] [-2 <param2>] <shader>\n");
+	exit(1);
+}
+
 int main(int argc, char *argv[]) {
-	if (argc != 2) {
-		fprintf(stderr, "Usage: glslview <shader>\n");
-		exit(1);
+	int width = 800, height = 800;
+
+	while (true) {
+		int c = getopt(argc, argv, "w:h:t:s:0:1:2:");
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'w':
+			width = atoi(optarg);
+			break;
+
+		case 'h':
+			height = atoi(optarg);
+			break;
+
+		case 't':
+			current_time = init_time = atof(optarg);
+			break;
+
+		case 's':
+			speed = atof(optarg);
+			init_speed = fabsf(speed);
+			break;
+
+		case '0':
+			param0 = init_param0 = atoi(optarg);
+			break;
+
+		case '1':
+			param1 = init_param1 = atoi(optarg);
+			break;
+
+		case '2':
+			param2 = init_param2 = atoi(optarg);
+			break;
+
+		default:
+			fprintf(stderr, "Invalid option '%c'\n", optopt);
+			usage();
+		}
 	}
 
+	if (argc - optind != 1)
+		usage();
+
 	SDL_Init(SDL_INIT_VIDEO);
 
 	SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
@@ -155,10 +230,10 @@ int main(int argc, char *argv[]) {
 	SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
 	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 
-	SDL_Window *window = SDL_CreateWindow("glslview", 0, 0, 800, 800, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
+	SDL_Window *window = SDL_CreateWindow("glslview", 0, 0, width, height, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
 	SDL_GLContext ctx = SDL_GL_CreateContext(window);
 
-	filename = argv[1];
+	filename = argv[optind];
 
 	init_watch();
 	init();
@@ -175,26 +250,32 @@ int main(int argc, char *argv[]) {
 				switch (e.key.keysym.sym) {
 				case SDLK_PAGEDOWN:
 					param0++;
+					print_params();
 					break;
 
 				case SDLK_PAGEUP:
 					param0--;
+					print_params();
 					break;
 
 				case SDLK_RIGHT:
 					param1++;
+					print_params();
 					break;
 
 				case SDLK_LEFT:
 					param1--;
+					print_params();
 					break;
 
 				case SDLK_DOWN:
 					param2++;
+					print_params();
 					break;
 
 				case SDLK_UP:
 					param2--;
+					print_params();
 					break;
 
 				case SDLK_ESCAPE:
@@ -207,7 +288,7 @@ int main(int argc, char *argv[]) {
 				break;
 
 			case SDL_MOUSEWHEEL:
-				speed /= pow(1.1, e.wheel.y);
+				set_speed(speed / pow(1.1, e.wheel.y));
 				break;
 
 			case SDL_QUIT:
diff --git a/glslwrite.c b/glslwrite.c
index 2913ae8..5b09c86 100644
--- a/glslwrite.c
+++ b/glslwrite.c
@@ -27,6 +27,7 @@
 
 #include <stdbool.h>
 #include <stdio.h>
+#include <unistd.h>
 
 #include <png.h>
 
@@ -36,12 +37,17 @@
 #include <SDL2/SDL_opengl.h>
 
 
+static float step = 20;
+static unsigned frame = 0;
+static unsigned max_frame = 0;
+
+
 static void savePNG(int width, int height, const char *output_dir) {
 	uint8_t pixels[width*height*4];
 	glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_INT_8_8_8_8, pixels);
 
 	char filename[strlen(output_dir) + 20];
-	snprintf(filename, sizeof(filename), "%s/%010u.png", output_dir, (unsigned)current_time);
+	snprintf(filename, sizeof(filename), "%s/%010u.png", output_dir, frame);
 
 	FILE *f = fopen(filename, "wb");
 	if (!f) {
@@ -84,12 +90,57 @@ static void savePNG(int width, int height, const char *output_dir) {
 	fclose(f);
 }
 
+static void usage(void) {
+	fprintf(stderr, "Usage: glslwrite [-w <width>] [-h <height>] [-s <step>] [-f <frames>] [-0 <param0>] [-1 <param1>] [-2 <param2>] <shader>\n");
+	exit(1);
+}
+
 int main(int argc, char *argv[]) {
-	if (argc != 3) {
-		fprintf(stderr, "Usage: glslwrite <shader> <output directory>\n");
-		exit(1);
+	int width = 800, height = 800;
+
+	while (true) {
+		int c = getopt(argc, argv, "w:h:s:f:0:1:2:");
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'w':
+			width = atoi(optarg);
+			break;
+
+		case 'h':
+			height = atoi(optarg);
+			break;
+
+		case 's':
+			step = atof(optarg);
+			break;
+
+		case 'f':
+			max_frame = atoi(optarg);
+			break;
+
+		case '0':
+			param0 = atoi(optarg);
+			break;
+
+		case '1':
+			param1 = atoi(optarg);
+			break;
+
+		case '2':
+			param2 = atoi(optarg);
+			break;
+
+		default:
+			fprintf(stderr, "Invalid option '%c'\n", optopt);
+			usage();
+		}
 	}
 
+	if (argc - optind != 2)
+		usage();
+
 	SDL_Init(SDL_INIT_VIDEO);
 
 	SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
@@ -97,14 +148,14 @@ int main(int argc, char *argv[]) {
 	SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
 	SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 
-	SDL_Window *window = SDL_CreateWindow("glslwrite", 0, 0, 800, 800, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
+	SDL_Window *window = SDL_CreateWindow("glslwrite", 0, 0, width, height, SDL_WINDOW_OPENGL|SDL_WINDOW_RESIZABLE);
 	SDL_GLContext ctx = SDL_GL_CreateContext(window);
 
-	filename = argv[1];
+	filename = argv[optind];
 	init();
 	load();
 
-	while (true) {
+	while (!max_frame || frame < max_frame) {
 		SDL_Event e;
 
 		while (SDL_PollEvent(&e)) {
@@ -128,8 +179,9 @@ int main(int argc, char *argv[]) {
 		render(width, height);
 		SDL_GL_SwapWindow(window);
 
-		savePNG(width, height, argv[2]);
-		current_time += 20;
+		savePNG(width, height, argv[optind+1]);
+		current_time += step;
+		frame++;
 	}
 
  quit: