OpenGL small drawing problem

Recommended Posts

Hi new opengl coder looking for some help. Basically ive drawn a rotatable box (gonna be a tank some day :p) and a circle around it to show its sort of collision detection. When I move it from the centre of the screen the circle becomes offset from the box as in the following screenies: piccy1 piccy2 piccy3 code:
                Gl.glPushMatrix();

Gl.glTranslatef(x, y, -1.01f);
Gl.glScalef(0.02f, 0.02f, 0.02f);
Gl.glRotatef(facing, 0, 0, 1);

Gl.glColor3f(1, 1, 1);
Gl.glVertex3f(-1.0f, 1.0f, 0.0f);
Gl.glVertex3f(1.0f, 1.0f, 0.0f);
Gl.glVertex3f(1.0f, -1.0f, 0.0f);
Gl.glVertex3f(-1.0f, -1.0f, 0.0f);
Gl.glEnd();

Gl.glPopMatrix();

Gl.glPushMatrix();

Gl.glTranslatef(x, y, -1.0f);
Gl.glScalef(0.02f, 0.02f, 0.02f);

float vectorX; float vectorY;

Gl.glBegin(Gl.GL_LINES);
Gl.glColor3f(1, 1, 1);
for (float angle = 0.0f; angle <= (2.0f * Math.PI); angle += 0.01f)
{
Gl.glVertex3f(vectorX, vectorY, 0.0f);

}
Gl.glEnd();

Gl.glPopMatrix();


I really cant see the cause. Seems like one object is behind the other? Any help is most welcome. :) [Edited by - tim-the-inventor on June 8, 2007 4:34:53 PM]

Share on other sites
I think that the problem may be that you seem to be generating your circle vertices around an offset origin when you have already had OpenGL offset the geometry. Perhaps try removing the "origin(X/Y) + " from your vectorX and -Y calculations.

Share on other sites
Thanks for quick reply, ive just realised how stupid that code was :p. Its updated and the offset is alot less but its still there.

Share on other sites
My pleasure - I'm glad that I helped. ^_^

As to your remaining offset, it occurs to me to ask: are you using a perspective or an orthographic projection? If the former, it could simply be that perspective projection is causing an apparent offset as a result of one element being placed slightly closer to the camera than the other (Gl.glTranslatef(x, y, -1.01f) as opposed to Gl.glTranslatef(x, y, -1.0f) (emphasis mine)).

If you are using a perspective projection, perhaps try placing both at the same distance from the camera.

Share on other sites
Thanks its fixed now. I made some small change to test and forgot to revert :]

Share on other sites
My pleasure - I'm glad that you got it working. ^_^

Create an account

Register a new account

• Partner Spotlight

• Forum Statistics

• Total Topics
627638
• Total Posts
2978327
• 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.
• 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?

• 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?

• 10
• 12
• 22
• 13
• 34