How to make 2d Chess Board in OpenGl - c++

Question

I have to make a 2d Chess Board of 8 * 8 blocks in OpenGL with VisualC++. I have the following code that i tried .
But I have a problem in this code .
I can't reduce the board size. e.g. 5*5.
When i click on the window it redraws the board.
I want to make this code to just work with loops. Except If , Else.
#include<GL\glut.h>
int black=0,white=1,color=0;
GLint a1=10,b1=10,a2=30,b2=30;
void init (void)
{
glClearColor (0.0, 0.0,1.0,0.0);
glMatrixMode (GL_PROJECTION);
glClear (GL_COLOR_BUFFER_BIT);
gluOrtho2D (0.0,120.0,0.0,140.0);
}
void lineSegment ()
{
for(int i=0;i<3;i++)
{
if(b2<120)
{
a1=10;b1=b2;
a2=30;b2=b2+20;
}
for(int j=0;j<5;j++)
{
if(a2<120)
{
if(color==black)
{
glColor3f(0,0,0);
glRecti(a1,b1,a2,b2);
color=1;
a1=a2;
a2=a2+20;
}
else
{
glColor3f(1,1,1);
glRecti(a1,b1,a2,b2);
color=0;
a1=a2;
a2=a2+20;
}
}
}
//GLint a1=10,b1=10,a2=30,b2=30;
}
glFlush();
}
void main (int argc, char** argv)
{
glutInit(&argc,argv); //Initialize GLUT.
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); // Set display mode.
glutInitWindowPosition (50,100); //Set top-left display-window position.
glutInitWindowSize (400,300); //Set display-window width and height.
glutCreateWindow ("An Example OpenGL Program"); //Create display window.
init(); // Execute initialization procedure.
glutDisplayFunc(lineSegment); //send graphics to display window.
glutMainLoop(); //display everything and wait.
}

Answer 1

Im going to suggest you significantly reduce the code you are working with. Define a width and height for the board and the number of divisions per side of the board.
Lets define width and height as w and h respectively and the number of divisions n and m respectively. w.l.o.g. assume n and m divide w and h evenly.
void DrawBoard(int w, int h, int n, int m) {
bool color = true;
int sw = w/n, sh = h/m; //square width and height respectively
//for each width and height draw a rectangle with a specific color
for(int i = 0; i < n; ++i) {
for(int j = 0; j < m; ++j) {
//oscillate the color per square of the board
if(color)
glColor3f(1, 1, 1);
else
glColor3f(0, 0, 0);
color = !color;
//draw a rectangle in the ith row and jth column
glRecti(i*sw, j*sh, (i+1)*sw, (j+1)*sh);
}
if(m % 2 == 0) color = !color; //switch color order at end of row if necessary
}
}
This should give the basic idea, though I might have hessed up an index or two. But essentially, iterate over the grid cells and draw a rectangle per board square.
This code will also draw the board starting at coordinate (0, 0) and finishing at (w, h). However if you would like it in an arbitrary position you can either add an (x, y) to eaxh corresponding coordinate in the glRecti call, or learn about transforms in openGL and use glTranslatef.