Jump to content
  • Advertisement
Sign in to follow this  

OpenGL gluPerspective still looks orthogonal, why?

This topic is 2804 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

Hi, i'm new to OpenGL and i'm trying to look at a flat tilemap slightly side-on. My approach is to rotate the view and render all the tiles, but i don't get any sort of depth distortion even after calling gluPerspective().

void gluPerspective_( GLdouble fovY, GLdouble aspect, GLdouble zNear, GLdouble zFar ) {
const GLdouble pi = 3.1415926535897932384626433832795;
GLdouble fH = tan( fovY / 360 * pi ) * zNear;
GLdouble fW = fH * aspect;
glFrustum( -fW, fW, -fH, fH, zNear, zFar );

/* Draw scene objects */
void renderGL() {
static float theta = 0.0f;
theta += delta;

// Clear and reset

// Render all map tiles (24x24)
glRotatef(theta, 1.0f, 0.0f, 0.0f);
glBindTexture(GL_TEXTURE_2D, textures[0]); // Tilemap texture (48x(48*n))
for (int x = -12; x < 12; x++) {
for (int y = -12; y < 12; y++) {
GLfloat tex = ((float)(rand() % 20)) / 20.0f; // Random tile
const GLfloat td = 1.0f / 20.0f;

glTexCoord2f(0.0f, tex+td);
glVertex3f(x / 12.0f, y / 12.0f, 0.0f);

glTexCoord2f(1.0f, tex+td);
glVertex3f((x+1) / 12.0f, y / 12.0f, 0.0f);

glTexCoord2f(1.0f, tex);
glVertex3f((x+1) / 12.0f, (y+1) / 12.0f, 0.0f);

glTexCoord2f(0.0f, tex);
glVertex3f(x / 12.0f, (y+1) / 12.0f, 0.0f);

// Render player
glBindTexture(GL_TEXTURE_2D, textures[1]); // Player's texture
int animstate = 0;
int direction = 0;
GLfloat x = direction / 4.0f;
GLfloat y = animstate / 4.0f;
const GLfloat d = 1.0f / 4.0f;

glTexCoord2f(x, y+d);
glVertex3f(0.0f, 0.0f, 0.0f);

glVertex3f(1.0f, 0.0f, 0.0f);

glVertex3f(1.0f, 1.0f, 0.0f);

glTexCoord2f(x, y);
glVertex3f(0.0f, 1.0f, 0.0f);


/* Flip to screen */


/* OpenGL Initialisation */
bool initGL() {
if (!loadTextures()) return false;
glViewport(0, 0, SCR_WIDTH, SCR_HEIGHT);

glClearColor(0.0f, 0.0f, 0.0f, 0.0f);


// Enable RGBA Alpha blending

// Set up projection matrix
gluPerspective_(180.0, ((double)SCR_WIDTH)/((double)SCR_HEIGHT), -10.0, 100.0);

// Set up Modelview matrix

// Wireframe mode
//glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

return true;

Apologies for the large code dump, but could anyone offer any insight?
The camera is looking down the default direction (down the Z axis).

Share this post

Link to post
Share on other sites
You need to check for opengl errors (glGetError) when you have unexpected behavior, it can help you figure out what's wrong.

I'm guessing that it's not working because you're specifying zNear as -10, when the docs for glFrustum specifies:

Specify the distances to the near and far depth clipping planes. Both distances must be positive. GL_INVALID_VALUE is generated if nearVal or farVal is not positive, or if left = right, or bottom = top, or near = far.

It probably sees the illegal value and just dumps the whole operation like you never called it.

Also if you're converting degrees to radians, doesn't this need to be two pi?
GLdouble fH = tan( fovY / 360 * pi ) * zNear;

Share this post

Link to post
Share on other sites
Ah, thank you, it seems to be working now. I changed the gluPerspective call to work between positive 0.1 and 5.0, and couldn't see anything. But since openGL looks down the -Z axis.. i changed the tilemap to render at Z=-1.0 instead of Z=0.0 and now everything works fine.

Thanks for the suggestion :)

My gluPerspective replacement is based of this.

Share this post

Link to post
Share on other sites
Sign in to follow this  

  • Advertisement

Important Information

By using GameDev.net, you agree to our community Guidelines, Terms of Use, and Privacy Policy.

We are the game development community.

Whether you are an indie, hobbyist, AAA developer, or just trying to learn, GameDev.net is the place for you to learn, share, and connect with the games industry. Learn more About Us or sign up!

Sign me up!