The program is meant to move the cube with inverted controls, so you feel like you are moving the camera around the cube.
I am unable to get the cube to appear.
/*
* SDL OpenGL Tutorial.
* (c) Michael Vance, 2000
* [email protected]
*
* Distributed under terms of the LGPL.
*/
#include <GL/glew.h>
#include <GL/gl.h>
#include <SDL2/SDL.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
static GLboolean should_rotate = GL_TRUE;
static void quit_tutorial(int code)
{
/*
* Quit SDL so we can release the fullscreen
* mode and restore the previous video settings,
* etc.
*/
SDL_Quit();
/* Exit program. */
exit(code);
}
static void handle_keys(const Uint8 *keys, GLfloat pos[3])
{
/*
* We're only interested if 'Esc' has
* been presssed.
*
* EXERCISE:
* Handle the arrow keys and have that change the
* viewing position/angle.
*/
if (keys[SDL_SCANCODE_ESCAPE])
quit_tutorial(0);
if (keys[SDL_SCANCODE_W])
{
pos[2] -= 0.3f;
}
if (keys[SDL_SCANCODE_A])
{
pos[0] -= 0.3f;
}
if (keys[SDL_SCANCODE_S])
{
pos[2] = 0.3f;
}
if (keys[SDL_SCANCODE_D])
{
pos[0] = 0.3f;
}
if (keys[SDL_SCANCODE_SPACE])
{
pos[1] = 0.3f;
}
if (keys[SDL_SCANCODE_LSHIFT])
{
pos[1] -= 0.3f;
}
}
static void process_events(GLfloat pos[3])
{
/* Our SDL event placeholder. */
SDL_Event event;
/* Grab all the events off the queue. */
while (SDL_PollEvent(&event))
{
switch (event.type)
{
case SDL_QUIT:
/* Handle quit requests (like Ctrl-c). */
quit_tutorial(0);
break;
}
//std::cout << "event" << std::endl;
}
handle_keys(SDL_GetKeyboardState(__null), pos);
}
static void draw_screen(SDL_Window *win, GLfloat pos[3])
{
/* Our angle of rotation. */
static float angle = 0.0f;
/*
* EXERCISE:
* Replace this awful mess with vertex
* arrays and a call to glDrawElements.
*
* EXERCISE:
* After completing the above, change
* it to use compiled vertex arrays.
*
* EXERCISE:
* Verify my windings are correct here ;).
*/
static GLfloat v0[] = {-1.0f, -1.0f, 1.0f};
static GLfloat v1[] = {1.0f, -1.0f, 1.0f};
static GLfloat v2[] = {1.0f, 1.0f, 1.0f};
static GLfloat v3[] = {-1.0f, 1.0f, 1.0f};
static GLfloat v4[] = {-1.0f, -1.0f, -1.0f};
static GLfloat v5[] = {1.0f, -1.0f, -1.0f};
static GLfloat v6[] = {1.0f, 1.0f, -1.0f};
static GLfloat v7[] = {-1.0f, 1.0f, -1.0f};
static GLubyte red[] = {255, 0, 0, 255};
static GLubyte green[] = {0, 255, 0, 255};
static GLubyte blue[] = {0, 0, 255, 255};
static GLubyte white[] = {255, 255, 255, 255};
static GLubyte yellow[] = {255, 255, 0, 255};
static GLubyte black[] = {0, 0, 0, 255};
static GLubyte cyan[] = {0, 255, 255, 255};
static GLubyte purple[] = {255, 0, 255, 0};
/* Clear the color and depth buffers. */
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
/* We don't want to modify the projection matrix. */
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
/* Move down the z-axis. */
glTranslatef(-pos[0], -pos[1], -pos[2]);
/* Rotate. */
glRotatef(angle, 0.0, 1.0, 0.0);
if (should_rotate)
{
if ( angle > 360.0f)
{
angle = 0.0f;
}
}
/* Send our triangle data to the pipeline. */
glBegin(GL_TRIANGLES);
glColor4ubv(red);
glVertex3fv(v0);
glColor4ubv(purple);
glVertex3fv(v1);
glColor4ubv(blue);
glVertex3fv(v2);
glColor4ubv(red);
glVertex3fv(v0);
glColor4ubv(blue);
glVertex3fv(v2);
glColor4ubv(white);
glVertex3fv(v3);
glColor4ubv(purple);
glVertex3fv(v1);
glColor4ubv(black);
glVertex3fv(v5);
glColor4ubv(cyan);
glVertex3fv(v6);
glColor4ubv(purple);
glVertex3fv(v1);
glColor4ubv(cyan);
glVertex3fv(v6);
glColor4ubv(blue);
glVertex3fv(v2);
glColor4ubv(black);
glVertex3fv(v5);
glColor4ubv(yellow);
glVertex3fv(v4);
glColor4ubv(green);
glVertex3fv(v7);
glColor4ubv(black);
glVertex3fv(v5);
glColor4ubv(green);
glVertex3fv(v7);
glColor4ubv(cyan);
glVertex3fv(v6);
glColor4ubv(yellow);
glVertex3fv(v4);
glColor4ubv(red);
glVertex3fv(v0);
glColor4ubv(white);
glVertex3fv(v3);
glColor4ubv(yellow);
glVertex3fv(v4);
glColor4ubv(white);
glVertex3fv(v3);
glColor4ubv(green);
glVertex3fv(v7);
glColor4ubv(white);
glVertex3fv(v3);
glColor4ubv(blue);
glVertex3fv(v2);
glColor4ubv(cyan);
glVertex3fv(v6);
glColor4ubv(white);
glVertex3fv(v3);
glColor4ubv(cyan);
SDL_PumpEvents();
glVertex3fv(v6);
glColor4ubv(green);
glVertex3fv(v7);
glColor4ubv(purple);
glVertex3fv(v1);
glColor4ubv(red);
glVertex3fv(v0);
glColor4ubv(yellow);
glVertex3fv(v4);
glColor4ubv(purple);
glVertex3fv(v1);
glColor4ubv(yellow);
glVertex3fv(v4);
glColor4ubv(black);
glVertex3fv(v5);
glEnd();
SDL_GL_SwapWindow(win);
//std::cout << pos[0] << std::endl;
}
static void setup_opengl(int width, int height)
{
float ratio = (float)width / (float)height;
/* Our shading model--Gouraud (smooth). */
glShadeModel(GL_SMOOTH);
/* Culling. */
glCullFace(GL_BACK);
glFrontFace(GL_CCW);
glEnable(GL_CULL_FACE);
/* Set the clear color. */
glClearColor(1, 0, 0, 1);
/* Setup our viewport. */
glViewport(0, 0, width, height);
/*
* Change to the projection matrix and set
* our viewing volume.
*/
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
/*
* EXERCISE:
* Replace this with a call to glFrustum.
*/
gluPerspective(100.0, ratio, 1.0, 1024.0);
}
int main(int argc, char *argv[])
{
int width = 640;
int height = 480;
if (SDL_Init(SDL_INIT_EVERYTHING) != 0)
{
printf("error initializing SDL: %s\n", SDL_GetError());
}
//glewExperimental = true;
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);
setup_opengl(width, height);
std::cout << (glGetError() == GL_NO_ERROR);
SDL_GL_SetSwapInterval( 1 );
SDL_Window *win = SDL_CreateWindow("Worlds", // creates a window
SDL_WINDOWPOS_CENTERED,
SDL_WINDOWPOS_CENTERED,
width, height, SDL_WINDOW_OPENGL);
SDL_GLContext context = SDL_GL_CreateContext(win);
GLfloat pos[] = {0, 0, 5};
while (1)
{
/* Process incoming events. */
process_events(pos);
/* Draw the screen. */
//printf("frame");
draw_screen(win, pos);
if (glGetError() != GL_NO_ERROR)
{
std::cout << glewGetErrorString(glGetError()) << std::endl;
}
SDL_Delay(1000/30);
}
SDL_GL_DeleteContext(context);
SDL_DestroyWindow(win);
return 0;
}
I am running this on Linux Mint 20, with a NVIDIA 1650Ti.
CodePudding user response：
The OpenGL context needs to be valid before any OpenGL API function can be used:
//setup_opengl(width, height);
//std::cout << (glGetError() == GL_NO_ERROR);
SDL_GL_SetSwapInterval( 1 );
SDL_Window *win = SDL_CreateWindow(...);
SDL_GLContext context = SDL_GL_CreateContext(win);
setup_opengl(width, height);
std::cout << (glGetError() == GL_NO_ERROR);