From d3adb5c325b61547b79e2b9f6b25bd467ed7da67 Mon Sep 17 00:00:00 2001
From: Muaz Ahmad <m.ahmed_2000@hotmail.com>
Date: Tue, 2 May 2023 15:44:33 +0500
Subject: [PATCH] Recreated most of basic gl functions and perspective

---
 opglwidget.cpp | 34 +++++++++++++++++++++++++++++++++-
 opglwidget.h   |  3 +++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/opglwidget.cpp b/opglwidget.cpp
index 0907b3d..280a79a 100644
--- a/opglwidget.cpp
+++ b/opglwidget.cpp
@@ -1,13 +1,45 @@
 #include "opglwidget.h"
 #include <GL/gl.h>
+#include <GL/glu.h>
 #include <math.h>
 
 void OPGLWidget::initializeGL() {
+	glClearDepth(1.0f);
+	glDepthFunc(GL_LESS);
+	glEnable(GL_DEPTH_TEST);
+	glShadeModel(GL_SMOOTH);
+	glMatrixMode(GL_PROJECTION);
+	glLoadIdentity();
+	glMatrixMode(GL_MODELVIEW);
+	glEnable(GL_LIGHTING);
+	glEnable(GL_LIGHT0);
+	GLfloat light_array[] = {0.4, 0.4, 0.4, 0.4};
+	GLfloat light_position[] = {10.0, 20.0, 10.0, 1.0};
+	glLightfv(GL_LIGHT0, GL_AMBIENT, light_array);
+	glLightfv(GL_LIGHT0, GL_DIFFUSE, light_array);
+	glLightfv(GL_LIGHT0, GL_SPECULAR, light_array);
+	glLightfv(GL_LIGHT0, GL_POSITION, light_position);
 	glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
 }
 
 void OPGLWidget::paintGL() {
-	glClear(GL_COLOR_BUFFER_BIT);
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+	glLoadIdentity();
+	reorient();
+}
+
+void OPGLWidget::reorient() {
+	float F_mag = pow(loc[0], 2) + pow(loc[1], 2) +pow(loc[2], 2);
+	GLfloat f[] = {-loc[0]/F_mag, -loc[1] / F_mag, -loc[2] / F_mag};
+
+	GLfloat s[] = {-f[2], 0, f[0]};
+	float s_mag = pow(s[0], 2) + pow(s[1], 2) + pow(s[2], 2);
+
+	GLfloat u[] = {(s[1] * f[2] - s[2] * f[1]) / s_mag, (s[0] * f[2] - s[2] * f[0]) / s_mag, (s[0] * f[1] - s[1] * f[0]) / s_mag};
+
+	const GLfloat m[] = {s[0], u[0], -f[0], 0, s[1], u[1], -f[1], 0, s[2], u[2], -f[2], 0, 0, 0, 0, 1};
+	glMultMatrixf(m);
+	glTranslatef(-loc[0], -loc[1], -loc[2]);
 }
 
 void OPGLWidget::resizeGL(int w, int h) {
diff --git a/opglwidget.h b/opglwidget.h
index 3a32627..180f9d3 100644
--- a/opglwidget.h
+++ b/opglwidget.h
@@ -8,4 +8,7 @@ protected:
 	void paintGL();
 	void initializeGL();
 	void resizeGL(int w, int h);
+	void reorient();
+
+	float loc[3] = {-10, 0, -10};
 };