add uniform variable to shader

3 files changed, 29 insertions, 3 deletions

diff --git a/main.c b/main.c
index 09cf2fb..c4da904 100644
--- a/main.c
+++ b/main.c
@@ -1,6 +1,8 @@
 #include <stdlib.h>
 #include <GL/glew.h>
 #include <GLFW/glfw3.h>
+#include <sys/time.h>
+#include <time.h>
 
 #include "shader.h"
 #include "die.h"
@@ -63,10 +65,21 @@ int main(int argc, char** argv) {
 		frag_shader(visuals_frag, visuals_frag_size)
 	);
 
+	// prepare uniform variables
+	GLint u_time = glGetUniformLocation(shader, "time");
+	int time_start = time(NULL);
+
 	// main draw loop
 	while (!glfwWindowShouldClose(window)) {
 		glfwPollEvents();
 
+		// set `time` uniform
+		struct timeval t;
+		gettimeofday(&t, NULL);
+		t.tv_sec -= time_start;
+		float time = t.tv_sec + (t.tv_usec / 1e6);
+		glUniform1f(u_time, time);
+
 		glUseProgram(shader);
 		glDrawArrays(GL_TRIANGLES, 0, 3);
 
diff --git a/makefile b/makefile
index fa39ee9..daf3750 100644
--- a/makefile
+++ b/makefile
@@ -4,6 +4,9 @@ LDFLAGS += -lGLEW
 
 CFLAGS += -g
 
+GLFLAGS += --target-env=opengl
+GLFLAGS += -fauto-map-locations
+
 .PHONY: FORCE
 .SECONDARY: # do not remove intermediate files
 
@@ -23,9 +26,9 @@ main.o: visuals_frag.h
 	./blob $< $*
 
 %_frag.spv: %.frag
-	glslc -o $@ $<
+	glslc $(GLFLAGS) -o $@ $<
 %_vert.spv: %.vert
-	glslc -o $@ $<
+	glslc $(GLFLAGS) -o $@ $<
 
 clean: FORCE
 	git clean -fxdi
diff --git a/visuals.frag b/visuals.frag
index 3539bdc..16e7712 100644
--- a/visuals.frag
+++ b/visuals.frag
@@ -2,7 +2,17 @@
 
 #include "config.h"
 
+uniform float time;
+
+// adapted from <https://www.shadertoy.com/view/4djSRW>
+float hash12(vec2 p) {
+	vec3 p3 = fract(vec3(p.xyx) * .1031);
+	p3 += dot(p3, p3.yzx + 33.33);
+	return fract((p3.x + p3.y) * p3.z);
+}
+
 void main() {
-	gl_FragColor = vec4(gl_FragCoord.x / WIDTH, gl_FragCoord.y / HEIGHT, 0, 1);
+	vec2 pos = gl_FragCoord.xy + time;
+	gl_FragColor = vec4(vec3(hash12(pos)), 1.0);
 }