Add cpp/opengl-cmake example for basic OpenGL project with CMake

cpp/opengl-cmake/CMakeLists.txt

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+###############################################################################
+## Author: Shaun Reed                                                        ##
+## Legal: All Content (c) 2021 Shaun Reed, all rights reserved               ##
+##                                                                           ##
+## Contact: shaunrd0@gmail.com  | URL: www.shaunreed.com | GitHub: shaunrd0  ##
+##############################################################################
+#
+
+# Define CMake version
+cmake_minimum_required(VERSION 3.15)
+
+project(
+    #[[NAME]]    OpenGL-Cmake
+    DESCRIPTION  "Example project for building OpenGL projects with CMake"
+    LANGUAGES    CXX
+)
+
+# Add test executable
+add_executable(opengl-test "test-gl.cpp")
+
+# Find OpenGL package
+find_package(OpenGL REQUIRED)
+if (OPENGL_FOUND)
+  # Link opengl-test executable to OpenGL
+  target_include_directories(opengl-test PUBLIC ${OPENGL_INCLUDE_DIR})
+  target_link_libraries(opengl-test PUBLIC ${OPENGL_LIBRARIES})
+
+else()
+  message(
+      "Error: CMake was unable to find the OpenGL package\n"
+      "Please install OpenGL and try again\n"
+  )
+endif()
+
+# Find GLUT package
+find_package(GLUT REQUIRED)
+if (GLUT_FOUND)
+  # Link opengl-test executable to GLUT
+  target_include_directories(opengl-test PUBLIC ${GLUT_INCLUDE_DIR})
+  target_link_libraries(opengl-test PUBLIC ${GLUT_LIBRARIES})
+
+else()
+  message(
+      "Error: CMake was unable to find the OpenGL package\n"
+      "Please install OpenGL and try again\n"
+  )
+endif()

cpp/opengl-cmake/test-gl.cpp

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+/*#############################################################################
+## Author: Shaun Reed                                                        ##
+## Requires freeglut3-dev to be installed with your package manager          ##
+## To build an executable: `g++ test-gl.cpp -w -lGL -lGLU -lglut -o test`    ##
+##                                                                           ##
+## Testing building OpenGL projects with source code from lazyfoo -          ##
+## https://lazyfoo.net/tutorials/OpenGL/                                     ##
+##############################################################################
+## test-gl.cpp
+*/
+
+#include <GL/freeglut.h>
+#include <GL/gl.h>
+#include <GL/glu.h>
+#include <stdio.h>
+
+//Screen constants
+const int SCREEN_WIDTH = 640;
+const int SCREEN_HEIGHT = 480;
+const int SCREEN_FPS = 60;
+
+//Color modes
+const int COLOR_MODE_CYAN = 0;
+const int COLOR_MODE_MULTI = 1;
+
+//The current color rendering mode
+int gColorMode = COLOR_MODE_CYAN;
+
+//The projection scale
+GLfloat gProjectionScale = 1.f;
+
+bool initGL()
+{
+  //Initialize Projection Matrix
+  glMatrixMode( GL_PROJECTION );
+  glLoadIdentity();
+  glOrtho( 0.0, SCREEN_WIDTH, SCREEN_HEIGHT, 0.0, 1.0, -1.0 );
+
+  //Initialize Modelview Matrix
+  glMatrixMode( GL_MODELVIEW );
+  glLoadIdentity();
+
+  //Initialize clear color
+  glClearColor( 0.f, 0.f, 0.f, 1.f );
+
+  //Check for error
+  GLenum error = glGetError();
+  if( error != GL_NO_ERROR )
+  {
+    printf( "Error initializing OpenGL! %s\n", gluErrorString( error ) );
+    return false;
+  }
+
+  return true;
+}
+
+void update()
+{
+
+}
+
+void render()
+{
+  //Clear color buffer
+  glClear( GL_COLOR_BUFFER_BIT );
+
+  //Reset modelview matrix
+  glMatrixMode( GL_MODELVIEW );
+  glLoadIdentity();
+
+  //Move to center of the screen
+  glTranslatef( SCREEN_WIDTH / 2.f, SCREEN_HEIGHT / 2.f, 0.f );
+
+  //Render quad
+  if( gColorMode == COLOR_MODE_CYAN )
+  {
+    //Solid Cyan
+    glBegin( GL_QUADS );
+    glColor3f( 0.f, 1.f, 1.f );
+    glVertex2f( -50.f, -50.f );
+    glVertex2f(  50.f, -50.f );
+    glVertex2f(  50.f,  50.f );
+    glVertex2f( -50.f,  50.f );
+    glEnd();
+  }
+  else
+  {
+    //RYGB Mix
+    glBegin( GL_QUADS );
+    glColor3f( 1.f, 0.f, 0.f ); glVertex2f( -50.f, -50.f );
+    glColor3f( 1.f, 1.f, 0.f ); glVertex2f(  50.f, -50.f );
+    glColor3f( 0.f, 1.f, 0.f ); glVertex2f(  50.f,  50.f );
+    glColor3f( 0.f, 0.f, 1.f ); glVertex2f( -50.f,  50.f );
+    glEnd();
+  }
+
+  //Update screen
+  glutSwapBuffers();
+}
+
+void handleKeys( unsigned char key, int x, int y )
+{
+  //If the user presses q
+  if( key == 'q' )
+  {
+    //Toggle color mode
+    if( gColorMode == COLOR_MODE_CYAN )
+    {
+      gColorMode = COLOR_MODE_MULTI;
+    }
+    else
+    {
+      gColorMode = COLOR_MODE_CYAN;
+    }
+  }
+  else if( key == 'e' )
+  {
+    //Cycle through projection scales
+    if( gProjectionScale == 1.f )
+    {
+      //Zoom out
+      gProjectionScale = 2.f;
+    }
+    else if( gProjectionScale == 2.f )
+    {
+      //Zoom in
+      gProjectionScale = 0.5f;
+    }
+    else if( gProjectionScale == 0.5f )
+    {
+      //Regular zoom
+      gProjectionScale = 1.f;
+    }
+
+    //Update projection matrix
+    glMatrixMode( GL_PROJECTION );
+    glLoadIdentity();
+    glOrtho( 0.0, SCREEN_WIDTH * gProjectionScale, SCREEN_HEIGHT * gProjectionScale, 0.0, 1.0, -1.0 );
+  }
+}
+
+void runMainLoop( int val );
+/*
+Pre Condition:
+ -Initialized freeGLUT
+Post Condition:
+ -Calls the main loop functions and sets itself to be called back in 1000 / SCREEN_FPS milliseconds
+Side Effects:
+ -Sets glutTimerFunc
+*/
+
+int main( int argc, char* args[] )
+{
+  //Initialize FreeGLUT
+  glutInit( &argc, args );
+
+  //Create OpenGL 2.1 context
+  glutInitContextVersion( 2, 1 );
+
+  //Create Double Buffered Window
+  glutInitDisplayMode( GLUT_DOUBLE );
+  glutInitWindowSize( SCREEN_WIDTH, SCREEN_HEIGHT );
+  glutCreateWindow( "OpenGL" );
+
+  //Do post window/context creation initialization
+  if( !initGL() )
+  {
+    printf( "Unable to initialize graphics library!\n" );
+    return 1;
+  }
+
+  //Set keyboard handler
+  glutKeyboardFunc( handleKeys );
+
+  //Set rendering function
+  glutDisplayFunc( render );
+
+  //Set main loop
+  glutTimerFunc( 1000 / SCREEN_FPS, runMainLoop, 0 );
+
+  //Start GLUT main loop
+  glutMainLoop();
+
+  return 0;
+}
+
+void runMainLoop( int val )
+{
+  //Frame logic
+  update();
+  render();
+
+  //Run frame one more time
+  glutTimerFunc( 1000 / SCREEN_FPS, runMainLoop, val );
+}