GLSL helloworld

Author: ssloy

Makefile

@@ -1,7 +1,7 @@
 SYSCONF_LINK = g++
 CPPFLAGS     =
 LDFLAGS      =
-LIBS         = -lm -lGL -lglut -lGLU
+LIBS         = -lm -lGL -lGLEW -lglut -lGLU
 
 DESTDIR = ./
 TARGET  = main

main.cpp

@@ -1,8 +1,14 @@
+#include <GL/glew.h>
 #include <GL/glu.h>
 #include <GL/glut.h>
+#include <iostream>
+#include <fstream>
 #include <vector>
 #include <cmath>
 
+#define USE_SHADERS 1
+GLuint  prog_hdlr;
+
 const int SCREEN_WIDTH  = 1024;
 const int SCREEN_HEIGHT = 1024;
 const float camera[]           = {.6,0,1};
@@ -31,6 +37,56 @@ void change_size(int w, int h) {
 	glMatrixMode(GL_MODELVIEW);
 }
 
+#if USE_SHADERS
+void printInfoLog(GLuint obj) {
+	int log_size = 0;
+	int bytes_written = 0;
+	glGetProgramiv(obj, GL_INFO_LOG_LENGTH, &log_size);
+	if (!log_size) return;
+	char *infoLog = new char[log_size];
+	glGetProgramInfoLog(obj, log_size, &bytes_written, infoLog);
+	std::cerr << infoLog << std::endl;
+	delete [] infoLog;
+}
+
+bool read_n_compile_shader(const char *filename, GLuint &hdlr, GLenum shaderType) {
+	std::ifstream is(filename, std::ios::in|std::ios::binary|std::ios::ate);
+	if (!is.is_open()) {
+		std::cerr << "Unable to open file " << filename << std::endl;
+		return false;
+	}
+	long size = is.tellg();
+	char *buffer = new char[size+1];
+	is.seekg(0, std::ios::beg);
+	is.read (buffer, size);
+	is.close();
+	buffer[size] = 0;
+
+	hdlr = glCreateShader(shaderType);
+	glShaderSource(hdlr, 1, (const GLchar**)&buffer, NULL);
+	glCompileShader(hdlr);
+	std::cerr << "info log for " << filename << std::endl;
+	printInfoLog(hdlr);
+	delete [] buffer;
+	return true;
+}
+
+void setShaders(GLuint &prog_hdlr, const char *vsfile, const char *fsfile) {
+	GLuint vert_hdlr, frag_hdlr;
+	read_n_compile_shader(vsfile, vert_hdlr, GL_VERTEX_SHADER);
+	read_n_compile_shader(fsfile, frag_hdlr, GL_FRAGMENT_SHADER);
+
+	prog_hdlr = glCreateProgram();
+	glAttachShader(prog_hdlr, frag_hdlr);
+	glAttachShader(prog_hdlr, vert_hdlr);
+
+	glLinkProgram(prog_hdlr);
+	std::cerr << "info log for the linked program" << std::endl;
+	printInfoLog(prog_hdlr);
+}
+#endif
+
+
 int main(int argc, char **argv) {
 	glutInit(&argc, argv);
 	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
@@ -49,6 +105,17 @@ int main(int argc, char **argv) {
 	glEnable(GL_LIGHT0);
 	glLightfv(GL_LIGHT0, GL_POSITION, light0_position);
 
+#if USE_SHADERS
+	glewInit();
+	if (GLEW_ARB_vertex_shader && GLEW_ARB_fragment_shader && GL_EXT_geometry_shader4)
+		std::cout << "Ready for GLSL - vertex, fragment, and geometry units" << std::endl;
+	else {
+		std::cout << "No GLSL support" << std::endl;
+		exit(1);
+	}
+	setShaders(prog_hdlr, "shaders/vert_shader.glsl", "shaders/frag_shader.glsl");
+	glUseProgram(prog_hdlr);
+#endif
 	glutMainLoop();
 	return 0;
 }

shaders/frag_shader.glsl

@@ -0,0 +1,22 @@
+#version 120
+
+varying vec3 n;
+
+void main(void) {
+    vec3 l = normalize(gl_LightSource[0].position.xyz);
+
+    float intensity = .2 + max(dot(l,normalize(n)), 0.0);
+
+    if (intensity > 0.95)
+        intensity = 1;
+    else if (intensity > 0.5)
+        intensity = .6;
+    else if (intensity > 0.25)
+        intensity = .4;
+    else
+        intensity = .2;
+
+    gl_FragColor = gl_Color * intensity;
+    return;
+}
+

shaders/vert_shader.glsl

@@ -0,0 +1,9 @@
+#version 120
+
+varying vec3 n;
+
+void main() {
+	gl_Position   = gl_ModelViewProjectionMatrix * gl_Vertex;
+	gl_FrontColor = gl_Color;
+    n = gl_NormalMatrix * gl_Normal;
+}