Add a uniform color.

src/main.cc

@@ -1,6 +1,7 @@
 #include <iostream>
 #include <epoxy/gl.h>
 #include <GLFW/glfw3.h>
+#include <cmath>
 
 void framebuffer_size_callback(GLFWwindow* window, int width, int height);
 void process_input(GLFWwindow* window);
@@ -11,11 +12,9 @@ const char* vertexShaderCode = R"(
 // Set the GLSL version to 3.3 and use the OpenGL core profile
 #version 330 core
 layout (location = 0) in vec3 aPos;
-out vec4 vertexColor;
 
 void main() {
 	gl_Position = vec4(aPos, 1.0);
-	vertexColor = vec4(0.5, 0.0, 0.0, 1.0);
 }
 )";
 
@@ -23,10 +22,11 @@ const char* fragmentShaderCode = R"(
 // Set the GLSL version to 3.3 and use the OpenGL core profile
 #version 330 core
 out vec4 FragColor;
-in vec4 vertexColor;
+
+uniform vec4 ourColor;
 
 void main() {
-	FragColor = vertexColor;
+	FragColor = ourColor;
 }
 )";
 
@@ -221,6 +221,13 @@ int main() {
 
 		// Use the shaderProgram shader program for drawing verticies.
 		glUseProgram(shaderProgram);
+
+		// Change the uniform color.
+		float timeValue = glfwGetTime();
+		float greenValue = (std::sin(timeValue) / 2.0f) + 0.5f;
+		int vertexColorLocation = glGetUniformLocation(shaderProgram, "ourColor");
+		glUniform4f(vertexColorLocation, 0.0f, greenValue, 0.0f, 1.0f);
+
 		if (!rectangleToggled) {
 			// Bind the state to use the vertexArrayObject object so OpenGL knows what to do with the verticies.
 			glBindVertexArray(triangleRenderObjs->vertexArrayObject);