diff --git a/sdfps.c b/sdfps.c
index e853fb4..a8a8a0d 100644
--- a/sdfps.c
+++ b/sdfps.c
@@ -59,10 +59,12 @@ void init(Sdfps* s) { /* TODO: Error checks */
 
 		/* viewport resolution (in pixels), z = 1 */
 		"uniform vec3 iResolution;\n"
+		/* playback time in seconds */
+		"uniform float iTime;\n"
 
 		"out vec4 out_color;\n"
 		"void main() {\n"
-			"vec2 xy = gl_FragCoord.xy;\n"
+			"vec2 xy = gl_FragCoord.xy + vec2(sin(iTime), cos(iTime));\n"
 			"out_color = vec4(sin(xy.x), sin(xy.y), sin(xy.x) + sin(xy.y), 1);\n"
 			"if(xy.x > iResolution.x / 2.0) out_color = out_color.zxyw;\n"
 		"}\n");
@@ -120,6 +122,7 @@ void render(Sdfps *s) {
 	GLuint iResolution = glGetUniformLocation(s -> shader_program, "iResolution");
 	// TODO: error check?
 	glUniform3f(iResolution, (f32) fb_w, (f32) fb_h, 1.0f);
+	glUniform1f(glGetUniformLocation(s -> shader_program, "iTime"), 0.001f * (f32) SDL_GetTicks());
 
 	glClearColor(0.1f, 0.25f, 0.24f, 1);
 	glClear(GL_COLOR_BUFFER_BIT);