HTML Canvas Coordinates







googletag.cmd.push(function() { googletag.display('div-gpt-ad-1422003450156-2'); });



HTML Canvas Coordinates



❮ Previous
Next ❯


Canvas Coordinates


The HTML canvas is a two-dimensional grid.


The upper-left corner of the canvas has the coordinates (0,0)


In the previous chapter, you saw this method used: fillRect(0,0,150,75).


This means: Start at the upper-left corner (0,0) and draw a 150x75 pixels rectangle.



Coordinates Example


Mouse over the rectangle below to see its x and y coordinates:



X

Y




Draw a Line


To draw a straight line on a canvas, use the following methods:



  • moveTo(x,y) - defines the starting point of the line

  • lineTo(x,y) - defines the ending point of the line


To actually draw the line, you must use one of the "ink" methods, like stroke().




Example




Your browser does not support the HTML5 canvas tag.

var c=document.getElementById("myCanvas2");
var canvOK=1;
try {c.getContext("2d");}
catch (er) {canvOK=0;}
if (canvOK==1)
{
var ctx=c.getContext("2d");
ctx.moveTo(0,0);
ctx.lineTo(200,100);
ctx.stroke();
}

Define a starting point in position (0,0), and an ending point in position (200,100).
Then use the stroke() method to actually draw the line:



var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.moveTo(0,0);
ctx.lineTo(200,100);
ctx.stroke();

Try it Yourself »







googletag.cmd.push(function() { googletag.display('div-gpt-ad-1493883843099-0'); });





Draw a Circle


To draw a circle on a canvas, use the following methods:



  • beginPath() - begins a path

  • arc(x,y,r,startangle,endangle) - creates an arc/curve. To create a circle with arc(): Set start angle to 0 and end angle to 2*Math.PI. The x and y parameters define the x- and y-coordinates of the center of the circle. The r parameter defines the radius of the circle.



Example



Your browser does not support the HTML5 canvas tag.

var c=document.getElementById("myCanvas3");
var canvOK=1;
try {c.getContext("2d");}
catch (er) {canvOK=0;}
if (canvOK==1)
{
var ctx=c.getContext("2d");
ctx.beginPath();
ctx.arc(95,50,40,0,2*Math.PI);
ctx.stroke();
}

Define a circle with the arc() method. Then use the stroke() method to actually draw the
circle:



var canvas = document.getElementById("myCanvas");
var ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.arc(95,50,40,0,2*Math.PI);
ctx.stroke();

Try it Yourself »




❮ Previous
Next ❯

-

Popular posts from this blog

How to check contact read email or not when send email to Individual?

Image
Clash Royale CLAN TAG #URR8PPP up vote 1 down vote favorite I'm using WordPress 4.9.8, CiviCRM to 5.5.1, I usually send email to contact by Search> Find contacts View contact details Action> Send email Send email ok, Contact received mail ok like picture But status only Email sent though contact read email or not. So, can CiviCRM can change status to Email read when contact read email? wordpress email share | improve this question asked Sep 26 at 0:12 ToanLuong 49 9 add a comment  |  up vote 1 down vote favorite I'm using WordPress 4.9.8, CiviCRM to 5.5.1, I usually send email to contact by Search> Find contacts View contact details Action> Send email Send email ok, Contact received mail ok like picture But status only Email sent though contact read email or not. So, can CiviCRM can change status to Email read when contact read email? wordpress email share | improve this questi...
Read more

Displaying single band from multi-band raster using QGIS

Image
Clash Royale CLAN TAG #URR8PPP 1 How can I extract a single band from multi-band raster in QGIS? I have an remote sensed image which has 6 bands (including NDVI band), I want to display each band separately, but have no idea how to do. I have seen some questions similar here but none worked for me. The original image (has 6 bands) is: I want to display the band 6 which should be like this: But I tried gdal_translate, and couldn't get the correct result. What I have got is: qgis raster multi-band share | improve this question edited Mar 5 at 0:53 Summer asked Mar 4 at 6:42 Summer Summer 23 6 Is this any help gis.stackexchange.com/questions/220658/… ? if not gis.stackexchange.com/questions/62133/… might help. – Michael Stimson Mar 4 at 6:46 Thanks for answering but when I used gdal_translate, qgis showed that 'Error 4: Kayena.tif: No such file or directory". Would you know how to fi...
Read more

How many registers does an x86_64 CPU actually have?

Image
Clash Royale CLAN TAG #URR8PPP up vote 2 down vote favorite I am currently learning reverse engineering and am studying the flags register. I had in my mind that rflags was just another name for one of the 16 general purpose registers, for example rax or rbx . But it looks like rflags is actually an additional register. So that makes 17 registers in total... how many more could there be? I have spent at least an hour on this and found numerous different answers. The best answer so far is this, which says that there are 40 registers in total. 16 General Purpose Registers 2 Status Registers 6 Code Segment Registers 16 SSE Registers 8 FPU/MMX Registers But if I add that up, I get 48. Could anybody provide an official answer on how many registers an x86_64 CPU has (e.g. an Intel i7). Additionally, I have seen references to 'hardware' and 'architectural' registers. What are those registers and how many are there? register x86-64 share | improve this...
Read more