I am a fairly new programmer and I am trying to make a very basic game using Java where you just move a sprite around the screen. What I have accomplished so far is make a SpriteSheet class that loads in my sprite sheet and saves a BufferedImage of the spritesheet as a field of that class and a Sprite class that will get a subimage(the sprite itself) from this field and saves it as a field in the Sprite class. I've tested this and it all works like it should. I understand this may not all be typical or the "correct", efficient way of doing things. I'm ok with figuring that out on my own but my problem now is understanding the relationship between BufferedImage, Graphics, and Canvas. I saw a tutorial where a guy saved his sprite as a BufferedImage and used this to create a Graphic. He then painted this Graphic onto a Canvas and added the Canvas to his JFrame. He also fit a BufferStrategy in there somehow connected to his Graphics, and I don't understand that at all. Whenever I try to adapt his method for my purposes, it never works. I've looked over the javadocs countless times for these things and I get them individually, but I just can't seem to understand how they fit together to accomplish my goals.
So in short: can anyone explain how BufferedImage, Graphics, and Canvas all fit together in the context of displaying a sprite for a 2D game, and how is a BufferStrategy used? Appropriate and relevant methods? Will this method be appropriate for rendering moving sprites around 15 fps? etc... My problem does not come from a lack of research or lack of knlowedge necessarily but more from a lack of understanding.
Thank you very much and any advice is greatly appreciated!
BufferedImage is a Image type, which has the capacity to be modified from within the code, but, it has no means by which it can paint it self to the screen.
Canvas is a AWT (heavy weight) container which is typically used for providing activate painting access via it's BufferStrategy. This is displayed to the screen.
Graphics is a abstract graphical library designed to make it easier to perform cross platform renderering.
The Canvas, via it's BufferStragegy provides access to a Graphics instance, which allows you to paint to the Canvas (and by extension, the screen). You use this Graphics context to paint the BufferedImage
A Canvas by itself can't be displayed on the screen, it must be first contained within a window of some type, like java.awt.Frame.
Essentially, the frame shows the user the Canvas, the Canvas provides access to the graphics hardware via the BufferStrategy and Graphics context and the BufferedImage provides a generalised representation of an image/image data which can be painted to the Graphics context (of the Canvas)
Maybe you should start by having a look at the JavaDocs for Canvas, BufferStrategy, BufferStrategy and BufferCapabilities and 2D Graphics for some examples
Related
I am developing a graphic project in java using swing and awt libraries. I am looking for a method that allow me to draw very fast on my JPanel. I tried various methods: overriding paintComponent, calling repaint(x, y, width, heigth).. But in all cases i have to repaint ALL the screen! I have a background and a small image in front of it that changes every few time. i am looking for a method that allow me to paint on the screen only the small image, i don't need to repaint the background too, because it is always the same, and the small image is always at the same coords. for example in C++ i painted the background and then i only painted the small images in front of it using putimage (graphics.h), so that it was very very fast. Do someone have some tips?
I've had some experience with game programming and usually a JPanel is used as canvas. Now to paint on it you would write a simple loop which continuously buffers an image and later paints it to the screen. So on initialisation you create a Graphics or Graphics2D object which is passed to a buffer() method. After painting a BufferedImage with the Instance of Graphics, some paint() method paints the BufferedImage to the screen.
When only painting the background once, previously drawn images will still be visible. If all your images are the same size, you don't have to bother but I still recommend repainting your background as well.
Have a look at the book Killer Game Programming In Java for further information, it's a great reference.
Tips:
Paint static images to a BufferedImage and then draw that within the paintComponent using Graphics#drawImage(...)
You do know that the repaint(...) method is overloaded and that one overload can accept a Rectangle parameter, limiting the area of repainting.
Ok, I'm not even sure if that is the right question to ask.
I've been confused by what is A Graphics object for a while now, I used to think that it is simplly a tool to use to change colors and draw to specific container(ie JFrame, JPanel).
However, I've been studying buffering(triple, double, flipping...etc) and how it works for 3 days now, and my confusion has only increased. for instance, why when we need to draw to the buffer(ie BufferStrategy, BufferedImage) we get its own graphics object to draw to it and then we project it to the screen? does the Graphics Object represent the drawing surface (ie the JPanel it self if we're using one to draw custom painting via JPanel#paintComponent(Graphics g)) ?
and so when we're getting the graphics object of a buffer, do we actually get its drawing surface to paint on?
Please somebody explain, any help is appreciated
Thanks
From the API:
A Graphics object encapsulates state information needed for the basic
rendering operations that Java supports. This state information
includes the following properties:
The Component object on which to draw.
A translation origin for rendering and clipping coordinates.
The current clip.
The current color.
The current font.
The current logical pixel operation function (XOR or Paint).
The current XOR alternation color (see setXORMode(java.awt.Color)).
So a Graphics instance contains information about WHERE to draw (a component) as well as HOW to draw it (a color, font, etc). It then gives you methods so you can tell it WHAT to draw (a rectangle, circle, text, etc).
I'm working on a project for maze generation using Java, swing, and Java2D. I'm fairly new to Java2D so please excuse me if this question is newbish.
Basically, I have a successfully generated maze. I wish to draw this maze on a custom JPanel that I've set up and properly overridden PaintComponent on. The problem I have now is I currently have the ability to draw the maze, but every time I repaint it disappears. I've solved this by having it redraw the maze every time repaint() is called but this seems horribly inefficient. Since the maze doesn't change why should I have to redraw it?
So my question is this: is there any way to "cache" the drawing of the maze so I don't have to waste cycles redrawing it every time? I can see redrawing it every time for exceptionally large mazes being a major source of slow downs.
Thank you!
Draw the maze to a BufferedImage. Then in your paintComponent() method just paint the BufferedImage. Swing will determine whether the entire maze or just parts of it need to be repainted.
For an example painting onto a BufferedImage see the DrawOnImage example from Custom Painting Approaches.
If the maze never changes, you can initially draw it into a BufferedImage. You can use your same code you wrote for overriding paintComponent by creating a BufferedImage and calling image.createGraphics() on it to get a Graphics2D object. Any painting you do to the Graphics2D object returned from createGraphics() is added to the BufferedImage. You may have to extract your previous drawing code just for the maze into its own function which takes a Graphics2D object and draws to it.
Once you have your maze drawn into the BufferedImage, you can use any of the drawImage() functions in Graphics or Graphics2D. This avoids having to redraw the maze: now you are just drawing the already rendered image.
I got two Graphics objects, is it possible to combine them into one?
The answer of Hovercraft Full of Eels is useful, but not what I meant. Say I have two Graphics objects, private Graphics gr1 and private Graphics gr2. Now, how should I merge them in the paintComponent(Graphics) method to draw them to my (for example JPanel)?
The question is not at all about images, but about mere Graphics objects. Sorry, the first paragraph was misleading.
Edit:
In response to Hovercraft Full of Eels:
If you draw in the paintComponent() method, I find it annoying everything is gone if you redraw your screen, and if you want to move something you have to save the coordinates and dimensions of everything, adjust those and get them someway in your Graphics object.
The question I asked myself was accely: What object is best suited or saving a Graphics object. A Graphics object, I thought. but the problem is that if you have (for example) two rectangles, and one moves to the left and one moves to the right you can't if you have 1 Graphics object.
My solution was multiple graphics objects, which can be transformed to simulate movement and then drawn to the screen.
#Hovercraft Full of Eels I think you (and most SO'ers) think this is not a good solution, looking at your answer.
But, an answer saying You're doing it all wrong, you'd better stop programming doesn't help me at all, so please give me an alternative.
You can draw any image into a BufferedImage by getting its Graphics context, drawing in it, and then disposing of the Graphics object. For example
// get a Graphics object from BufferedImage, img1
Graphics g = img1.getGraphics();
// use that g to draw another BufferedImage starting at x, y of 0, 0
g.drawImage(img2, 0, 0, null);
// clean up resources so as not to run out.
g.dispose();
Now img1 shows old img1 with img2 overlying it. If you want the images to be transparent, you'll need to read up on alpha composite and how to use it
Edit
Regarding your edited question:
I got two Graphics objects, is it possible to combine them into one?
The answer of Hovercraft Full of Eels is useful, but not what I meant. Say I have two Graphics objects, private Graphics gr1 and private Graphics gr2. Now, how should I merge them in the paintComponent(Graphics) method to draw it to my (for example JPanel)?
The question is not at all about images, but about mere Graphics objects. Sorry, the first paragraph was misleading.
This request is somewhat confusing to me since I think of Graphics objects as pens or paintbrushes that are used to draw something to an image or the screen. So I don't think that you draw a Graphics object to anything, but rather that you use a Graphics object as a tool to draw to something else that can display or store the graphics. You are going to have to put a lot more effort into asking your question, supplying us with enough details so that we don't have to keep guessing what it is you are trying to do. Please tell us the whole story.
Edit 2
In response to your latest edit to your question:
If you draw in the paintComponent() method, I find it annoying everything is gone if you redraw your screen, and if you want to move something you have to save the coordinates and dimensions of everything, adjust those and get them someway in your Graphics object.
The question I asked myself was accely: What object is best suited or saving a Graphics object. A Graphics object, I thought. but the problem is that if you have (for example) two rectangles, and one moves to the left and one moves to the right you can't if you have 1 Graphics object.
No, a better solution I think is to use a BufferedImage to save that which should persist. When ever you wanted to add an image to the background BufferedImage, you'd obtain the BufferedImage's Graphics object by calling getGraphics() on it, then you'd draw your image to it by using the Graphics object's drawImage(...) method, then you'd call dispose() on the BufferedImage's Graphics object so as not to lose resources.
To draw the background BufferedImage in the background, you'd call it at the top of the paintComponent(...) method, usually just after calling the super.paintComponent(...) method.
My solution was multiple graphics objects, which can be transformed to simulate movement and then drawn to the screen.
#Hovercraft Full of Eels I think you (and most SO'ers) think this is not a good solution, looking at your answer.
Yep, you guess correctly -- I believe that there are better solutions than the one you suggest.
An example of just what I'm getting at can be found in my code post in my answer to this question: changing-jpanel-graphics-g-color-drawing-line.
If you run my code, you'd see this:
To impose images, use an appropriate layout, as shown here.
To compose images, use an appropriate composite rule, as shown here.
Addendum: #HFOE is correct. An instance of Graphics or Graphics2D, sometimes called a graphics context, is a transitory means to apply rendering methods; the target device or off-screen image must exist independently. Classes implementing the Shape interface are good candidates for encapsulating information about what to render in a given context. AffineTest and GraphPanel are examples.
I have trouble understanding a fundamental concept in Java 2D.
To give a specific example:
One can customize a swing component via implementing it's own version of the method paintComponent(Graphics g)
Graphics is available to the body of the method.
Question:
What is exactly this Graphics object, I mean how it is related to the object that has the method paintComponent? Ok, I understand that you can do something like:
g.setColor(Color.GRAY);
g.fillOval(0, 0, getWidth(), getHeight());
To get a gray oval painted. What I can not understand is how is the Graphics object related to the component and the canvas. How is this drawing actually done?
Another example:
public class MyComponent extends JComponent {
protected void paintComponent(Graphics g) {
System.out.println("Width:"+getWidth()+", Height:"+getHeight());
}
public static void main(String args[]) {
JFrame f = new JFrame("Some frame");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setSize(200, 90);
MyComponent component = new MyComponent ();
f.add(component);
f.setVisible(true);
}
}
This prints
Width:184, Height:52
What does this size mean? I have not added anything to the frame of size(200,90).
UPDATE:
I understand that I must override paint to give in the Graphics g object the hints required to do the repaint and that I do not have to create a Graphics object as one will be given by platform.
What happens after that is what I can not understand.
E.g. does Graphics represent the screen and the object is painted accordingly on screen as soon as I start calling the various g.setXXX methods?
Does it get stored in a queue and there is a 1-1 association among g and each component? So the framework uses each g of each component to paint it one at a time?
How does this work?
Any help on this is highly welcome
Thanks
I understand your problem as I struggled with it for some time when I was learning Java graphics. It's not just Java 2D graphics - it is part of AWT.
When you create a JFrame or some other top-level object, it does a lot of work "behind the scenes" - part of which is creating a Graphics object. (There is not explicit notification of this, though if you stepped through the code with a debugger you may see classes which create the Graphics).
You then create components which you add, or register with, the top-level object. These all have to implement a call-back method, including
paint(Graphics g);
You will then #Override these methods so that when the component is rendered it uses YOUR paint method.
Do not try to save the Graphic or create a new one. Think of it as the framework taking the responsibility off you.
The size of components is often taken out of your hands. If you use a layout manager then it may decide to resize your component.
If you are coming from a procedural imperative background you may well have problems (I came from FORTRAN). My advice would be to try a number of tutorials and - at some stage - enlightenment will start to come.
The general documentation for Java graphics is poor. There are many concepts which are opaque (see How does Java Graphics.drawImage() work and what is the role of ImageObserver ). The early implementation was rushed through and had many bugs. Even now it is often unclear whether and in what order you should call methods such as setPack() and setVisible().
This doesn't mean you shouldn't use it! Just that the learning curve is a bit longer than IMO it should be.
MORE:
Also YOU don't decide when something is painted, the framework does. paint(g) really means "The framweork is repainting its components. What to you want this component to provide at this stage".
Maybe providePaintingInstructionsWhenRequiredForComponentGraphics(Graphics g) would be a useful name.
Similarly repaint() does not repaint at your orders, but when the system thinks it should. I haven't found it useful.
If you (say) resize a component interactively every slight change will normally trigger a paint(g). try putting a LOG.debug() in the paint code and seeing when it gets called.
What does this size mean? I have not added anything to the frame of size(200,90).
You added your component to the frame and set the size of the frame to be (200, 90). The default layout manager for the content pane of the frame is the BorderLayout, which means the component you added gets all the available space. The frame needs some space for the title bar and borders, so your component gets the remaining space.
The component does not create a static Graphics object association.
The graphics object is the wrapper for a platform handle giving access to a physical device, like the screen. It's valid for the time when "paint" is executed only, you can't store it and reuse it later. It is a resource managed by the "toolkit".
The component itself is an abstraction on top of the windowing system, that gets asociated shortly with this device for getting rendered.
EDIT
You can force such an association calling "getGraphics" if you feel the need to paint out of the "paint" callback. This should be a very rare case and you ALWAYS should dispose the Graphics afterwards.
Think of a Graphics like a piece of paper which you draw on to show how the Component looks like at that moment. After you've drawn it, the framework toolkit will trim off the edges and show what you've drawn to display the component. Moreover, the next time you draw the component, you'll be drawing on a different piece of paper, so don't keep the old Graphics around.