Coordinates - Revision history

Lerc: /* x,y Coordinates */

2017-06-21T00:28:39Z

‎x,y Coordinates

121.74.249.71: /* x,y Coordinates */

2015-07-23T07:50:24Z

‎x,y Coordinates

Lerc at 00:03, 26 April 2012

2012-04-26T00:03:40Z

Lerc at 00:56, 31 January 2012

2012-01-31T00:56:44Z

Lerc: Created page with "What exactly does this line mean? drawCircle(50,60,30) It is easy enough to figure out what the function is for. drawCircle quite clearly indicate that if you want to dra..."

2012-01-31T00:54:48Z

Created page with "What exactly does this line mean? drawCircle(50,60,30) It is easy enough to figure out what the function is for. drawCircle quite clearly indicate that if you want to dra..."

New page

What exactly does this line mean?
drawCircle(50,60,30)
It is easy enough to figure out what the function is for. drawCircle quite clearly indicate that if you want to draw a circle you've probably come to the right place. But what of the three numbers passed to the function. The things the drawCircle command needs to know is how big to draw the circle and where to draw the circle.

The last number is easy. That's how big the circle is. The first two numbers work as a pair to indicate position.

===x,y Coordinates===
The two values indicating position are traditionally named X and Y. The only reason the names X and Y are used is they were convenient letters at the end of the alphabet, they weren't doing much at the time so people decided to use them to stop them being so lazy.

The x coordinate is used to say how far <em>across</em> something is.
the y coordinate is used to say how far <em>down</em> something is.

As a pair the values 0,0 indicate the top-left corner. Which is to say 0 from the left and 0 from the top.
The pair 50, 200 would indicate a position 50 from the left and 200 from the top.

Mathematicians often use the bottom-left corner and move up. Ignore them, they're wrong :-P.

To help you understand This program draws horizontal and vertical lines showing the x and y positions.
<edcode>var x = 320;
var y = 240;

function move(){
x=x+1;
if (x > 640) x=0;

y=y+1
if (y > 480) y=1;
}

function draw(){
clear();

setColour("red");
drawLine(x,0,x,1000);
print ("X: "+x, x,20);

setColour("purple");
drawLine(0,y,1000,y);
print ("Y: "+y, 20,y);

setColour("black");
drawCircle(x,y,10);

}

run(move,draw);

</edcode>

@@ Line 14: / Line 14: @@
 The pair 50, 200 would indicate a position 50 from the left and 200 from the top.
-Mathematicians often use the bottom-left corner and move up.  Ignore them, they're wrong :-P.
+In Mathematics coordinates often use the bottom-left corner and move up and to the right.  If negative values are used it is common to start in the center.  In computer graphics it is more common to start at the top left of the display.
 To help you understand This program draws horizontal and vertical lines showing the x and y positions.

@@ Line 24: / Line 24: @@
    if (x > 640) x=0;
-   y=y+1
+   y=y+1;
    if (y > 480) y=1;
+}
@@ Line 41: / Line 41: @@
    setColour("black");
    drawCircle(x,y,10);
-−
+}

@@ Line 1: / Line 1: @@
 What exactly does this line mean?
      drawCircle(50,60,30)
-It is easy enough to figure out what the function is for.  drawCircle quite clearly indicate that if you want to draw a circle you have probably come to the right place, but what of the three numbers passed to the function.  The things the drawCircle command needs to know is how big to draw the circle and where to draw the circle.
+It is easy enough to figure out what the function is for.  drawCircle quite clearly indicates that if you want to draw a circle you have probably come to the right place, but what of the three numbers passed to the function.  The things the drawCircle command needs to know is how big to draw the circle and where to draw the circle.
 The last number is easy.  That's how big the circle is.  The first two numbers work as a pair to indicate position.