Chessboard in opengl - c++

Question

I'm trying to create 5x5 chessboard in OpenGL. I have been able to design a 5x6, and 8x8 but the code just won't work for the 5x5.
Can someone look over the code and maybe point out where my mistake is as the width just wont change to 5?
Here is the part of the code i seem to have a problem with:
void drawScene()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(-2.5*1.5, 0.0, 2.5*1.5);
for(double j=0.0;j>(-5*1.5);j-=1.5)
{
k++;
for(i=0.0;i<(2.5*3.0);i+=3.0)
{
if(k%2!=0)
{
glPushMatrix();
glTranslatef(i,0.0,j);
glCallList(_displayListId_blackArea);
glPopMatrix();
}
else
{
glPushMatrix();
glTranslatef(i+1.5,0.0,j);
glCallList(_displayListId_blackArea);
glPopMatrix();
}
}
}
for(double j=0.0;j>(-5*1.5);j-=1.5)
{
k++;
for(i=0.0;i<(2.5*3.0);i+=3.0)
{
if(k%2!=0)
{
glPushMatrix();
glTranslatef(i,0.0,j);
glCallList(_displayListId_whiteArea);
glPopMatrix();
}
else
{
glPushMatrix();
glTranslatef(i+1.5,0.0,j);
glCallList(_displayListId_whiteArea);
glPopMatrix();
}
}
}
}

Answer 1

If you have an odd number of columns, your "odd vs. even" for black vs white will go different than if you have an even number. I think the easiest way is to do one loop for all the Squares, and keep a bool white_or_black variable that is set to white_or_black = !white_or_black at the end of each loop.
There is also a large amount of duplicated code that could be made much simpler by having one loop rather than two.
[I'm not 100% sure what is going wrong in your code, so I'm not sure if this will ACTUALLY fix the problem - but I believe it's a worthwhile improvement].

Answer 2

Understand your problem first. You have to draw odd vs even for black vs white board that means at first row if you draw odd white board then you have to draw even black board and in next row even white board and odd black board. For completing 5*5 chessboard pattern for white and black board row wise is given below:
3*2
2*3
3*2
2*3
3*2
But code you provide is for equal number of white and black board so you have to change the logic.Here is the part of code where I used my logic to draw 5*5 chessboard and its works perfectly.
for(float j=0.0;j>(-5*1.5);j-=1.5)
{
k++;
//for(i=0.0;i<(4*3.0);i+=3.0)
//{
if(k%2==0)
{
for(i=0.0;i<(3*3.0);i+=3.0){
glPushMatrix();
glTranslatef(i,0.0,j);
glCallList(_displayListId_blackArea);
glPopMatrix();
}
}
else
{
for(i=0.0;i<(2*3.0);i+=3.0){
glPushMatrix();
glTranslatef(i+1.5,0.0,j);
glCallList(_displayListId_blackArea);
glPopMatrix();
}
}
//}
}
k=0;
for(float j=0.0;j>(-5*1.5);j-=1.5)
{
k++;
//for(i=0.0;i<(4*3.0);i+=3.0)
//{
if(k%2!=0)
{
for(i=0.0;i<(3*3.0);i+=3.0){
glPushMatrix();
glTranslatef(i,0.0,j);
glCallList(_displayListId_whiteArea);
glPopMatrix();
}
}
else
{
for(i=0.0;i<(2*3.0);i+=3.0){
glPushMatrix();
glTranslatef(i+1.5,0.0,j);
glCallList(_displayListId_whiteArea);
glPopMatrix();
}
}
}
k=0;
glutSwapBuffers();
}

Answer 3

I suspect that by "the width won't change to 5", you are observing a width of 4 or 6. Would that be correct? It's quite likely in that case to be an error due to double-precision arithmetic.
You see, you assume infinite precision in your loops, but it's quite conceivable that 5*1.5 is not the same as adding 1.5 five times.
What you should really do is have an integer loop from 1 to 5 (or 0 to 4), and then multiply that value by your square size to produce a co-ordinate. It's generally not a good idea to loop over doubles unless you know what you are doing and what can happen.
Another thing that you should PLEASE do is use constants instead of literals. Instead of peppering your code with the number 5, why not define:
const int BoardWidth = 5;
const int BoardHeight = 5;
Then it will be a lot easier to change.

Answer 4

Forget that code, it has bad potential, you should use ints as a counter to create the board. For example:
const unsigned BOARD_SIZE = 5;
for(unsigned i = 0; i < BOARD_SIZE; ++i){
for(unsigned j = 0; j < BOARD_SIZE; ++j){
drawBoardCell(i,j, (i*BOARD_SIZE + j) % 2 == 0);
}
}
void drawBoardCell(const int row, const int col, const bool isBlack){
glPushMatrix();
glTranslatef(col+1.5,0.0,row);
const int callId = isBlack ? _displayListId_blackArea : _displayListId_whiteArea;
glCallList(callId);
glPopMatrix();
}
That might not work at first try but it should give you a starting point.