I have written some code to experiment with opengl programming on Ubuntu, its been a little while but I used to have a reasonable understanding of C. Since c++ i’m told is the language of choice for games programming I am trying to develop with it.
This is my first real attempt at opengl with sdl and I have gotten to this far, it compiles and runs but my camera function doesn’t seem to do anything. I know there is probably a lot better ways to do this sort of stuff but I wanted to get the basics before I moved on to more advanced stuff.
main.cpp
#include <iostream>
#include <cmath>
#include "SDL/SDL.h"
#include "SDL/SDL_opengl.h"
int screen_width = 640;
int screen_height = 480;
const int screen_bpp = 32;
float rotqube = 0.9f;
float xpos = 0, ypos = 0, zpos = 0, xrot = 0, yrot = 0, angle=0.0;
float lastx, lasty;
SDL_Surface *screen = NULL; // create a default sdl_surface to render our opengl to
void camera (void) {
glRotatef(xrot,1.0,0.0,0.0); // x-axis (left and right)
glRotatef(yrot,0.0,1.0,0.0); // y-axis (up and down)
glTranslated(-xpos,-ypos,-zpos); // translate the screen to the position
SDL_GL_SwapBuffers();
}
int DrawCube(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glTranslatef(0.0f, 0.0f,-7.0f);
glRotatef(rotqube,0.0f,1.0f,0.0f);
glRotatef(rotqube,1.0f,1.0f,1.0f);
glBegin(GL_QUADS);
glColor3f(0.0f,1.0f,0.0f);
glVertex3f( 1.0f, 1.0f,-1.0f);
glVertex3f(-1.0f, 1.0f,-1.0f);
glVertex3f(-1.0f, 1.0f, 1.0f);
glVertex3f( 1.0f, 1.0f, 1.0f);
glColor3f(1.0f,0.5f,0.0f);
glVertex3f( 1.0f,-1.0f, 1.0f);
glVertex3f(-1.0f,-1.0f, 1.0f);
glVertex3f(-1.0f,-1.0f,-1.0f);
glVertex3f( 1.0f,-1.0f,-1.0f);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f( 1.0f, 1.0f, 1.0f);
glVertex3f(-1.0f, 1.0f, 1.0f);
glVertex3f(-1.0f,-1.0f, 1.0f);
glVertex3f( 1.0f,-1.0f, 1.0f);
glColor3f(1.0f,1.0f,0.0f);
glVertex3f( 1.0f,-1.0f,-1.0f);
glVertex3f(-1.0f,-1.0f,-1.0f);
glVertex3f(-1.0f, 1.0f,-1.0f);
glVertex3f( 1.0f, 1.0f,-1.0f);
glColor3f(0.0f,0.0f,1.0f);
glVertex3f(-1.0f, 1.0f, 1.0f);
glVertex3f(-1.0f, 1.0f,-1.0f);
glVertex3f(-1.0f,-1.0f,-1.0f);
glVertex3f(-1.0f,-1.0f, 1.0f);
glColor3f(1.0f,0.0f,1.0f);
glVertex3f( 1.0f, 1.0f,-1.0f);
glVertex3f( 1.0f, 1.0f, 1.0f);
glVertex3f( 1.0f,-1.0f, 1.0f);
glVertex3f( 1.0f,-1.0f,-1.0f);
glEnd();
SDL_GL_SwapBuffers();
rotqube +=0.9f;
return true;
}
bool init_sdl(void)
{
if( SDL_Init( SDL_INIT_EVERYTHING ) != 0 )
{
return false;
}
SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
// TODO: Add error check to this screen surface init
screen = SDL_SetVideoMode( screen_width, screen_height, screen_bpp, SDL_OPENGL | SDL_HWSURFACE | SDL_RESIZABLE );
return true;
}
static void init_opengl()
{
float aspect = (float)screen_width / (float)screen_height;
glViewport(0, 0, screen_width, screen_height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, aspect, 0.1, 100.0);
glMatrixMode(GL_MODELVIEW);
glClearColor(0.0, 0.0 ,0.0, 0);
glEnable(GL_DEPTH_TEST);
}
void heartbeat()
{
float xrotrad, yrotrad;
int diffx, diffy;
SDL_Event event;
while(1)
{
while(SDL_PollEvent(&event))
{
switch(event.type)
{
case SDL_KEYDOWN:
switch(event.key.keysym.sym)
{
case SDLK_ESCAPE:
exit(0);
break;
case SDLK_w:
yrotrad = (yrot / 180 * 3.141592654f);
xrotrad = (xrot / 180 * 3.141592654f);
xpos += (float)sin(yrotrad);
zpos -= (float)cos(yrotrad);
ypos -= (float)sin(xrotrad);
std::cout << "w pressed" << std::endl;
break;
case SDLK_s:
yrotrad = (yrot / 180 * 3.141592654f);
xrotrad = (xrot / 180 * 3.141592654f);
xpos -= (float)sin(yrotrad);
zpos += (float)cos(yrotrad);
ypos += (float)sin(xrotrad);
break;
case SDLK_d:
yrotrad = (yrot / 180 * 3.141592654f);
xpos += (float)cos(yrotrad) * 0.2;
zpos += (float)sin(yrotrad) * 0.2;
break;
case SDLK_a:
yrotrad = (yrot / 180 * 3.141592654f);
xpos -= (float)cos(yrotrad) * 0.2;
zpos -= (float)sin(yrotrad) * 0.2;
break;
default:
break;
}
break;
case SDL_MOUSEMOTION:
diffx=event.motion.x-lastx; //check the difference between the current x and the last x position
diffy=event.motion.y-lasty; //check the difference between the current y and the last y position
lastx=event.motion.x; //set lastx to the current x position
lasty=event.motion.y; //set lasty to the current y position
xrot += (float)diffy; //set the xrot to xrot with the addition of the difference in the y position
yrot += (float)diffx; //set the xrot to yrot with the addition of the difference in the x position
break;
case SDL_QUIT:
exit(0);
break;
case SDL_VIDEORESIZE:
screen = SDL_SetVideoMode( event.resize.w, event.resize.h, screen_bpp, SDL_OPENGL | SDL_HWSURFACE | SDL_RESIZABLE );
screen_width = event.resize.w;
screen_height = event.resize.h;
init_opengl();
std::cout << "Resized to width: " << event.resize.w << " height: " << event.resize.h << std::endl;
break;
default:
break;
}
}
DrawCube();
camera();
SDL_Delay( 50 );
}
}
int main(int argc, char* argv[])
{
if( init_sdl() != false )
{
std::cout << "SDL Init Successful" << std::endl;
}
init_opengl();
std::cout << "Hello World" << std::endl;
heartbeat(); // this is essentially the main loop
SDL_Quit();
return 0;
}
Makefile
all:
g++ -o test main.cpp -lSDL -lGL -lGLU
It compiles and runs, I guess I just need some help with doing the camera translation. Thanks
Remove the glLoadIdentity() call from DrawCube(). Replace it with glPushMatrix() at the beginning and glPopMatrix() at the end. Now pressing ‘w’ does something. (I am not entirely sure what it is supposed to do.)
The problem is glLoadIdentity clears all the previous transformations set up with glTranslatef and the like. Detailed description: http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/pushmatrix.html