How can i fill text in the canvas with mutiple font.
I can be able to fill in canvas this:
This is an example of what I want to do
this is another example of what I want to do
I know that i can slpit the sting and do first fill the normal text, second the bold text, and third the rest of the text. but i want to be able to drag and drop the text, so i cant do in that way.
Sorry, you're out of luck. There's no easy way out here.
You have to call drawtext at least three times if you want text with a bolded word in the center.
There may be a time in the future where you are allowed to draw arbitrary html, the spec mentions this is a real possibility, but that won't be for some time. To quote the spec:
Note: A future version of the 2D context API may provide a way to render fragments of documents, rendered using CSS, straight to the canvas. This would be provided in preference to a dedicated way of doing multiline layout.
From the end of this section.
You can of course still drag and drop, you just have to have a list of elements and their locations that make up a "node". Much more complicated objects have been done in the canvas no doubt.
Related
when we use Google vision's DOCUMENT_TEXT_DETECTION for a image, it decides what are the blocks in the image and what texts are in each block
Here I want to get the text for the blocks which are defined by me(already have a model to identify different blocks in a image).
Simply I want the texts within blocks defined by me but the defined by Google vision.
How I can achieve this?
For now, I decided to filter symbols for given block's vertices. It is better, if there is a way to simply find intersected symbols. For, now I'm going to loop through every symbol.
I found a better way to do this. First I merge each block vertically and between every block it is possible to include textual separator. It mean after every block there is a line of text. So then we can provide this image with merged blocks as the input for Google vision API. Is the response we can get full text for our input and we also have the text that we previously set between the blocks. So we can split the whole text using that. Then we can have block-wise text
I would like to face a problem for which I haven't seen a solution looking around in Internet. This is: I need to save the elements drawn by WEB users on a canvas space not as a flat image, but each one singularly. This in order to let the same user, or even other users, to modify every single element (drag-and-drop, erase, erase partially, ecc.) in a second moment. This should also help to eventually save a drawing history and restore it in next working sessions. All the examples I found were intended to save just a canvas flat image.
Update:
To better clarify: not necessary as layers, but for sure I thought to realize several different driving tools; a drawing element is the singular application/istance of a tool: a circle, a box, a added image, a straight line or even a free hand drawing that start from the moment of right button mouse click till it is released. Then the chance to save the elements state allowing to modify each one in a second moment.
You can't do this natively with canvas. You should look at using a third party library. Fabric is a library that was built to do what you want.
The base idea was to use convans as a container for vectorial shapes (triangles, squares, cirlces, etc.), manual drawn figures (see example http://www.williammalone.com/articles/create-html5-canvas-javascript-drawing-app/) and inserted images giving the chance to users to save/upload the content not as serialized image, but with each distinguished element in its original format in order to continue to work on them in a future work session.
My question is not language based or OS based. I guess every system is offering some sort of TextOut(text, x, y) method. I am looking for some guidlines or articles how should I implement selection of outputed text. Could not find any info about this.
The only thing which comes to my mind is like this:
When user clicks some point on the text canvas I know the coordinates of this point. I need to calculate where exactly it will be in my text buffer. So I am traversing from the begining of the buffer and I am applying to each character (or block of text) a style (if it has any). After this, I know that after given style the letter has given size. I am adding its width and height to previously calculated X,Y coordinates. In this way, I am traversing the buffer until the calculated position has not reached the point that has been clicked by the user. After I reach the point within range of some offset I have starting point for the selection.
This is the basic idea. I don't know if this is good, I would like to know how this is done for real like for example in Firefox. I know I could browse the sources and if I won't have a choice I'll do it. But first I am trying to find some article about it...
Selecting text is inherently specific to the control which is containing it and the means it stores that text.
A very simple (though questionably inefficient means) is to run the text flow algorithm you are using when clicking on a point and stopping the algorithm when you have reached what is closest to that point. More advanced controls might cache the text layout to make selections or drawing their content more efficient. Depending on how much you value CPU time or memory there are ways to use caches and special cases to make this “hit test” cheaper.
If you can make any assertions (only one font in the control, so every line has the same height) then it is possible to make these tests cheaper by indexing the font layout by lines and then doing simple arithmetic to find out which line was clicked on. If your text control is also using monospace fonts (every character occupies the same width as well as height) then you are in even more luck, as you can jump straight to the character information via a lookup table and two simple divisions.
Keep in mind that writing a text control from scratch is obscenely difficult. For best practice, you should keep the content of the document separate from the display information. The reason for this is because the text itself will need to be edited quite often, so algorithms such as Ropes or Gap Buffers may be employed on the data side to provide faster insertion around the caret. Every time text is edited it must also be rendered, which involves taking that data and running it through some kind of formatting / flow algorithms to determine how it needs to be displayed to the user. Both of these sides require a lot of algorithms that may be annoying to get right.
Unfortunately using the native TextOut functions will not help you. You will need to use methods which give you the text extents for individual characters, and more advanced (multiline for example) controls often must do their own rendering of characters using this information. Functions like TextOut are not built to deal with blinking insertion carets for example, or performing incremental updates on text layouts. While some TextOut style functions may support word wrap and alignment for you, they also require re-rendering the entire string which becomes more undesirable in proportion to the amount of text you need to work with in your control.
You are thinking at a much lower level than necessary (not an insult. you are thinking that you need to do much more work then you need to). Most (if not all) languages with GUI support will also have some form of selectionRange that gives you either the string that was selected or the start and stop indices in the string.
With a modern language, you should never have to calculate pixels and character widths.
For text selection in Javascript, see this question: Understanding what goes on with textarea selection with JavaScript
I'm currently working on a pure html 5 canvas implementation of the "flying tag cloud sphere", which many of you have undoubtedly seen as a flash object in some pages.
The tags are drawn fine, and the performance is satisfactory, but there's one thing in the canvas element that's kind of breaking this idea: you can't identify the objects that you've drawn on a canvas, as it's just a simple flat "image"..
What I have to do in this case is catch the click event, and try to "guess" which element was clicked. So I have to have some kind of matrix, which stores a link to a tag object for each pixel on the canvas, AND I have to update this matrix on every redraw. Now this sounds incredibly inefficient, and before I even start trying to implement this, I want to ask the community - is there some "well known" algorithm that would help me in this case? Or maybe I'm just missing something, and the answer is right behind the corner? :)
This is called the point location problem, and it's one of the basic topics in computational geometry. There are a lot of methods you could use that would be much faster than the approach you're thinking of, but the details depend on what exactly you want to accomplish.
For example, each text string is contained in a bounding box. Do you just want to test whether the user clicked somewhere in that box? Then simply store the minimum and maximum coordinates of each rendered string, and test the point against each bounding box to see if it's contained in that range. If you have a large number of points to test, you can build any number of data structures to speed this up (e.g. R-trees), but for a single point the overhead of constructing such a structure probably isn't worthwhile.
If you care about whether the point actually falls within the opaque area of the stroked characters, the problem is slightly trickier. One solution would be to use the bounding box approach to first eliminate most of the possibilities, and then render the remaining strings one at a time to an offscreen buffer, checking each time to see if the target point has been touched.
I'm thinking of making an application where at some points a graph is displayed that maps people over time and space. The vertical access is location, the horizontal access is time, and each person is identified by a line. At any point where the person did something of significance, there is a bigger dot on their line. Conceptually, clicking the dot brings up data about that particular dot, but clicking anywhere else on the line brings you to a detail on that person. Hypothetically, when you hover over the line the line should change color, and when you hover over a dot, just the dot should change color.
I know that I could do this pretty easily with flash, but I was wondering if these days there is any way to do this using only html and javascript. Is it possible? (Compatibility is not an issue, the only machine I am targeting is my own.)
Thanks!
You can do this with canvas, but it might be simpler to use SVG.
Since SVG uses DOM, you get builtin methods for handling events like clicking etc., instead of having to write your own handling code like you would need with canvas.
There are a few libraries that make working with SVG simpler and cross-browser compatible, such as Raphael and Dojo's dojox.gfx library.
You could create the dots as overlaid divs, so you can easily handle clicks etc. You'd have to sort out positioning quite neatly, of course.
However, highlighting the line will involve calculating the point-to-line distance manually and redrawing.