# Bug in logic for creating checkerboard grid

**URL:** https://discourse.processing.org/t/bug-in-logic-for-creating-checkerboard-grid/29759
**Category:** Coding Questions
**Created:** [April 30, 2021, 9:08pm UTC](https://discourse.processing.org/t/bug-in-logic-for-creating-checkerboard-grid/29759 "2021-04-30T21:08:09Z")
**Posts on this page:** 3
**Page:** 1

<div class="post-metadata">

### Author: ![rikitiki](https://avatars.discourse-cdn.com/v4/letter/r/65b543/32.png) [@rikitiki](https://discourse.processing.org/u/rikitiki)
#### Post date: [April 30, 2021, 9:08pm UTC](https://discourse.processing.org/t/bug-in-logic-for-creating-checkerboard-grid/29759/1 "2021-04-30T21:08:09Z")

</div>

Hello,

I’m hoping someone can find the flaw in my logic here. My goal is to create an even overlay checkerboard that has a transparency of 50. Here is my code in setup:

```auto
background(255);
int fillColor = 0;

int gridDimensions = 32;

for (int i = 0; i < gridDimensions; i++) {
  if (gridDimensions % 2 == 0)fillColor ^= 1;
  for (int j = 0; j < gridDimensions; j++) {
    fillColor ^= 1;
    fill(fillColor*255, 50);
    rect(i*gridDimensions,
      j*gridDimensions,
      i*gridDimensions+width/gridDimensions,
      j*gridDimensions+height/gridDimensions);
  }
}

```

My result is unexpected. Here’s the image I get and I’m unsure where I went wrong.

 ![Screen Shot 2021-04-30 at 2.06.49 PM](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/2X/f/f0e6b0039bf57bc4fcaeeb03dd7c33fac2ffbd59.jpeg)

---

<div class="post-metadata">

### Author: ![Chrisir](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/chrisir/32/45_2.png) [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [April 30, 2021, 9:12pm UTC](https://discourse.processing.org/t/bug-in-logic-for-creating-checkerboard-grid/29759/2 "2021-04-30T21:12:54Z")

</div>

the **two last** parameters of rect() are its width and height

Chrisir

```auto
    rect(i*gridDimensions, 
      j*gridDimensions, 
      width/gridDimensions - 5, 
      height/gridDimensions - 5);

```

---

<div class="post-metadata">

### Author: ![rikitiki](https://avatars.discourse-cdn.com/v4/letter/r/65b543/32.png) [@rikitiki](https://discourse.processing.org/u/rikitiki)
#### Post date: [April 30, 2021, 9:20pm UTC](https://discourse.processing.org/t/bug-in-logic-for-creating-checkerboard-grid/29759/3 "2021-04-30T21:20:25Z")

</div>

Thank you for helping me out of my brain derp. Brain wanted the last two params to be ending x and y point of the rect. 🙏

The following code now works:

```auto
background(255);
int fillColor = 0;

int gridDimensions = 32;

for (int i = 0; i < gridDimensions; i++) {
  if (gridDimensions % 2 == 0)fillColor ^= 1;
  for (int j = 0; j < gridDimensions; j++) {
    fillColor ^= 1;
    fill(fillColor*255, 50);
    rect(
      i*width/gridDimensions,
      j*height/gridDimensions,
      width/gridDimensions,
      height/gridDimensions);
  }
}

```