Sign in to follow this  
clicku

OpenGL gluPerspective still looks orthogonal, why?

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
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// Render all map tiles (24x24)
glLoadIdentity();
glRotatef(theta, 1.0f, 0.0f, 0.0f);
glBindTexture(GL_TEXTURE_2D, textures[0]); // Tilemap texture (48x(48*n))
glBegin(GL_QUADS);
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);
}
}
glEnd();

// Render player
glLoadIdentity();
glBindTexture(GL_TEXTURE_2D, textures[1]); // Player's texture
glBegin(GL_QUADS);
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);

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

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

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

glEnd();

/* Flip to screen */
SDL_GL_SwapBuffers();

}

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

glEnable(GL_TEXTURE_2D);
glShadeModel(GL_SMOOTH);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClearDepth(1.0f);

glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);

// Enable RGBA Alpha blending
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_BLEND);

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

// Set up Modelview matrix
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

// 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:

Quote:
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

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Partner Spotlight

  • Forum Statistics

    • Total Topics
      627643
    • Total Posts
      2978362
  • Similar Content

    • By xhcao
      Before using void glBindImageTexture(    GLuint unit, GLuint texture, GLint level, GLboolean layered, GLint layer, GLenum access, GLenum format), does need to make sure that texture is completeness. 
    • By cebugdev
      hi guys, 
      are there any books, link online or any other resources that discusses on how to build special effects such as magic, lightning, etc. in OpenGL? i mean, yeah most of them are using particles but im looking for resources specifically on how to manipulate the particles to look like an effect that can be use for games,. i did fire particle before, and I want to learn how to do the other 'magic' as well.
      Like are there one book or link(cant find in google) that atleast featured how to make different particle effects in OpenGL (or DirectX)? If there is no one stop shop for it, maybe ill just look for some tips on how to make a particle engine that is flexible enough to enable me to design different effects/magic 
      let me know if you guys have recommendations.
      Thank you in advance!
    • By dud3
      How do we rotate the camera around x axis 360 degrees, without having the strange effect as in my video below? 
      Mine behaves exactly the same way spherical coordinates would, I'm using euler angles.
      Tried googling, but couldn't find a proper answer, guessing I don't know what exactly to google for, googled 'rotate 360 around x axis', got no proper answers.
       
      References:
      Code: https://pastebin.com/Hcshj3FQ
      The video shows the difference between blender and my rotation:
       
    • By Defend
      I've had a Google around for this but haven't yet found some solid advice. There is a lot of "it depends", but I'm not sure on what.
      My question is what's a good rule of thumb to follow when it comes to creating/using VBOs & VAOs? As in, when should I use multiple or when should I not? My understanding so far is that if I need a new VBO, then I need a new VAO. So when it comes to rendering multiple objects I can either:
      * make lots of VAO/VBO pairs and flip through them to render different objects, or
      * make one big VBO and jump around its memory to render different objects. 
      I also understand that if I need to render objects with different vertex attributes, then a new VAO is necessary in this case.
      If that "it depends" really is quite variable, what's best for a beginner with OpenGL, assuming that better approaches can be learnt later with better understanding?
       
    • By test opty
      Hello all,
       
      On my Windows 7 x64 machine I wrote the code below on VS 2017 and ran it.
      #include <glad/glad.h>  #include <GLFW/glfw3.h> #include <std_lib_facilities_4.h> using namespace std; void framebuffer_size_callback(GLFWwindow* window , int width, int height) {     glViewport(0, 0, width, height); } //****************************** void processInput(GLFWwindow* window) {     if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)         glfwSetWindowShouldClose(window, true); } //********************************* int main() {     glfwInit();     glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);     glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);     glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);     //glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);     GLFWwindow* window = glfwCreateWindow(800, 600, "LearnOpenGL", nullptr, nullptr);     if (window == nullptr)     {         cout << "Failed to create GLFW window" << endl;         glfwTerminate();         return -1;     }     glfwMakeContextCurrent(window);     if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))     {         cout << "Failed to initialize GLAD" << endl;         return -1;     }     glViewport(0, 0, 600, 480);     glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);     glClearColor(0.2f, 0.3f, 0.3f, 1.0f);     glClear(GL_COLOR_BUFFER_BIT);     while (!glfwWindowShouldClose(window))     {         processInput(window);         glfwSwapBuffers(window);         glfwPollEvents();     }     glfwTerminate();     return 0; }  
      The result should be a fixed dark green-blueish color as the end of here. But the color of my window turns from black to green-blueish repeatedly in high speed! I thought it might be a problem with my Graphics card driver but I've updated it and it's: NVIDIA GeForce GTX 750 Ti.
      What is the problem and how to solve it please?
  • Popular Now