Opengl creating a 3d box instead of a simple triangle [closed] - c++

Question

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Closed 10 years ago.
I wrote the code below in C++ using Opengl library, it gives me a simple triangle on the screen (2d)
how can i change the code in the render function to write a 3d box or primitive object?
the code is below:
#include <iostream>
#include <GLUT/GLUT.h>
#include <OpenGL/OpenGL.h>
void render(void);
int main(int argc, char ** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
glutInitWindowPosition(100,100);
glutInitWindowSize(800,600);
glutCreateWindow("Welcome");
glutDisplayFunc(render);
glutMainLoop();
return 0;
}
void render(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glBegin(GL_POLYGON);
glColor3f(0.0,1.0,0.0);
glVertex2f(-0.5, -0.5);
glColor3f(1.0,0.0,0.0);
glVertex2f(0.5,0.0);
glColor3f(0.0,0.0,1.0);
glVertex2f(0.0,0.5);
glEnd();
glutSwapBuffers();
}

Answer 1

As a follow-up to Denis's answer...
If you are willing to learn a bit more OpenGL (perhaps a tall order if you just want to draw a cube...) here is the code that I reuse when doing small demos. It uses vertex array+buffer objects and creates a textured rectangular prism centered at (0, 0, 0). You'll need to provide your own texture.
The code to generate the rectangular prism is:
void GLmakeRect(GLuint vao, GLuint vbo[2], float w, float h, float d, GLuint storageHint) {
/*
8|---|9
0|BAC|1
10|---|---|---|12
|LEF|TOP|RIG|
11|---|---|---|13
3|FRO|2
4|---|5
|BOT|
6|---|7
*/
float verts[] = {
-0.5*w, 0.5*h, -0.5*d, 1.0/3.0, 0.25,
0.5*w, 0.5*h, -0.5*d, 2.0/3.0, 0.25,
0.5*w, 0.5*h, 0.5*d, 2.0/3.0, 0.5,
-0.5*w, 0.5*h, 0.5*d, 1.0/3.0, 0.5,
-0.5*w, -0.5*h, 0.5*d, 1.0/3.0, 0.75,
0.5*w, -0.5*h, 0.5*d, 2.0/3.0, 0.75,
-0.5*w, -0.5*h, -0.5*d, 1.0/3.0, 1.0,
0.5*w, -0.5*h, -0.5*d, 2.0/3.0, 1.0,
-0.5*w, -0.5*h, -0.5*d, 1.0/3.0, 0.0,
0.5*w, -0.5*h, -0.5*d, 2.0/3.0, 0.0,
-0.5*w, -0.5*h, -0.5*d, 0.0, 0.25,
-0.5*w, -0.5*h, 0.5*d, 0.0, 0.5,
0.5*w, -0.5*h, -0.5*d, 1.0, 0.25,
0.5*w, -0.5*h, 0.5*d, 1.0, 0.5
};
int polys[] = {
0, 3, 1, 1, 3, 2, // TOP
3, 4, 2, 2, 4, 5, // FRONT
4, 6, 5, 5, 6, 7, // BOTTOM
8, 0, 9, 9, 0, 1, // BACK
10, 11, 0, 0, 11, 3, // LEFT
1, 2, 12, 12, 2, 13 // RIGHT
};
glBindVertexArray(vao);
glBindBuffer(GL_ARRAY_BUFFER, vbo[0]);
glBufferData(GL_ARRAY_BUFFER, sizeof(verts), &verts[0], storageHint);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5*sizeof(float), 0);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5*sizeof(float), (void*)(3*sizeof(float)));
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo[1]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(polys), &polys[0], storageHint);
}
You can call the function like this during initialization:
GLuint vao, vbo[2]
glGenVertexArrays(1, &vao);
glGenBuffers(2, &vbo[0]);
GLmakeRect(vao, vbo, 1, 1, 1, GL_STATIC_DRAW);
To draw the cube in your render loop, do:
glBindTexture(GL_TEXTURE_2D, yourTextureHandleHere);
glBindVertexArray(vao);
glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_INT, 0);

Answer 2

If you just like to display a simple cube, take a look at "glutSolidCube" (and, maybe, the other "glutSolidABC" functions): glutSolidCube
But, when displaying 3d objects, you have to setup a projection matrix, a world matrix (transformation of the "viewer" or "camera") and, if you like to transform your objects, a model matrix for each object.
Some good kickstart lessons can be found at lighthouse3d.com in the "tutorials -> glut" section.
If you like to create your own meshes (a cube, sphere, etc) you have to write a mesh or surface class, which contains vertices and indices. When a rendercall appears, this class has to draw all of its vertices and triangles - your cube / sphere / etc.