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rodar3

OpenGL OpenGL glTranslatef problems

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Hi,

I've been doing some OpenGL with SDL and I'm slowing moving towards programming the camera movement to match that of an FPS. Basically what I have so far is a triangle being rendered in front of the viewport and I wanted to make the camera move forward (or any way really) to the triangle and then slowly add more directions. Basically taking it one step at a time.

 

Here's the problem. It won't move. No matter what I do, I can't seem to get the camera to translate anywhere. I've looked online and I can't seem to pinpoint where my mistake(s) are. I'll be continuing to look for the answer but I thought it might be really simple and someone could help me out here.

 

Here's my code...

 

[source]#include "SDL.h"
#include <windows.h>
#include <GL/gl.h>
#include <GL/glu.h>

#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480

// Variables
float moveZ = 0.0;

float camX = 0.0;
float camY = 0.0;
float camZ = 0.0;

void init()
{
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glClearColor(0.0, 0.0, 0.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
// Left Right Bottom Top
glOrtho(0.0, SCREEN_WIDTH, 0.0, SCREEN_HEIGHT, 1.0, -1.0);
glPushMatrix();
}

void triangle()
{
//draw triangle
glBegin(GL_TRIANGLES);
glVertex3f(320.0, 320.0, 0.0);
glVertex3f(200.0, 160.0, 0.0);
glVertex3f(400.0, 160.0, 0.0);
glEnd();
}

void moveCamera()
{
glLoadIdentity();
glTranslatef(camX, camY, camZ);
SDL_GL_SwapBuffers();
}

int main(int argc, char** args)
{
int quit = 0;
SDL_Event event;

SDL_Init(SDL_INIT_EVERYTHING);
SDL_SetVideoMode(640, 480, 32, SDL_OPENGL);
init();
triangle();
SDL_GL_SwapBuffers();

while(quit == 0)
{
if(SDL_PollEvent(&event))
{
if(event.type == SDL_KEYDOWN)
{
switch(event.key.keysym.sym)
{
case SDLK_w: camZ += 500.0; break;
}
}
else if(event.type == SDL_QUIT)
{
quit = 1;
}
}
moveCamera();
}

//SDL_Delay(2000);
SDL_Quit();
return 0;
}[/source]

 

Thanks for any help. smile.png

Edited by rodar3

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You have to draw the triangle after moving it. You will have to clear the frame buffer before drawing it also or the previous triangle will interfere with the new one.

Edited by Brother Bob

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Thanks a lot Bob. I did some reorganizing of my code and now I have something that is probably translating in some form except I have a new problem.

 

Now when I start the program the triangle shows up in front of me and I press the W key a few times to go forward. It seems as though nothing happens, the triangle doesn't change size or anything. Then all of a sudden, after pressing it a couple of times the screen goes blank. So I must be doing something wrong, and I've looked at a million tutorials and I can't seem to get anything to work. Help please :(.

 

[source]#include "SDL.h"
#include  <windows.h>
#include  <GL/gl.h>.h>
#include  <GL/glu.h>.h>
#include  <stdio.h>

#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480

// Variables
float moveZ = 0.0;

float camX = 0.0;
float camY = 0.0;
float camZ = 0.0;

int quit = 0;
SDL_Event event;

void init()
{
glViewport(0.0, 0.0, SCREEN_WIDTH, SCREEN_HEIGHT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
// Left Right Bottom Top
glOrtho(0.0, SCREEN_WIDTH, 0.0, SCREEN_HEIGHT, 10.0, -10.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glPushMatrix();
glClearColor(0.0, 0.0, 0.0, 1.0);
}

void moveCamera()
{
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glLoadIdentity();
glTranslatef(camX, camY, camZ);
glPushMatrix();
}

void render()
{
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glPopMatrix();
glPushMatrix();

glBegin(GL_TRIANGLES);
glVertex3f(320.0, 320.0, -5.0);
glVertex3f(200.0, 160.0, -5.0);
glVertex3f(400.0, 160.0, -5.0);
glEnd();

SDL_GL_SwapBuffers();
}

void eventCheck()
{
if(SDL_PollEvent(&event))
{
if(event.type == SDL_KEYDOWN)
{
switch(event.key.keysym.sym)
{
case SDLK_w: camZ += 1.0; break;
}
}
else if(event.type == SDL_QUIT)
{
quit = 1;
}
}
}

int main(int argc, char** args)
{
SDL_Init(SDL_INIT_EVERYTHING);
SDL_SetVideoMode(640, 480, 32, SDL_OPENGL);
init();
render();
printf("Should be triangle");

while(quit == 0)
{
eventCheck();
moveCamera();
render();
}

//SDL_Delay(2000);
SDL_Quit();
return 0;
}[/source].h>.h>

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Read up on orthographic projections, the whole point is that things wont change in size, the far and near plane values are probably culling the triangle after you move back.

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