Develop Reference

Draw shapes in Java based off if/else statements and action listener

I'm trying to figure out if there's any way to draw images (drawRect(), drawOval(), etc.) based on if/else statements or by using an ActionListener.
I don't want to post the complete problem because this is for an assignment, but for my own scenario:
If I have a button on a JPanel named "draw rectangle" and I have the x, y, width, and height from user input, is there any way I can attach an actionListener to "draw rectangle" that could somehow draw the rectangle using those values (passed by reference?).
I know I can use paintComponent, but I can't put that into the ActionListener and it seems to do things of its own accord and not based on a specific user's actions.
I don't really have any code for this because I can't figure out how to do it at all.

If I have a button on a
JPanel named "draw rectangle" and I have the
x, y, width, and height from user input, is there any way I can attach
an actionListener to "draw rectangle" that could somehow draw the
rectangle using those values (passed by reference?).
The short answer is yes.
Generally, you'll need to save the rectangle instructions in a model, and have the JPanel redraw the model when any of the shape buttons are pressed.
Let's take your rectangle example. What do you need to know to draw a rectangle on a JPanel? You need a starting point (upper left) and an ending point (lower right). You can use a java.awt.Point to hold the starting and ending point. You can set the thickness of the line, in pixels. You can set the color of the rectangle, using a JColorChooser. You can also set the rectangle to be an outline or filled with the chosen color.
That description will be similar for a line and a triangle. A circle is a little different, with a center point and a radius. As you can see, we already have a lot of information to keep track of just with these simple geometric shapes.
Then there's the issue of the drawing surface itself. It's possible to have a drawing surface larger than your computer screen can show. You can put the drawing surface inside of a JScrollPane.
All of these things must be determined so you can build the model of your application. You do this before you build the view using Swing components and the controller using action listeners.

Libgdx Spritebatch bug

however, i have a weird issue, when drawing, it seems the outside 1px of an image is stretched to fit a rectangle, but the inside is only stetched to an extend, i was drawing to 48x48 tiles, but drew a 500x500 tile to show the issue. [ 500x500 draws fine ]
the worst part seems to be, it chooses when to stretch and not to stretch. and also what to strech. im sorry this is hard to explain but i have attached a image that i hope does a better job.
it could just be misunderstanding how to use a draw with spritebatch
edit: Tile is 48x48 not 64x64, ive just been working all day.

This is because you are not rendering "pixel perfect" which means your image does not line up with the pixel grid of your monitor. A quick fix might be to set a linear filter for your textures, since by default it uses nearest and thus a pixel on the screen will inherit the closest color it can get. A linear filter will interpolate colors and make that line "look" thinner.
texture.setFilter(Texture.TextureFilter.Linear, Texture.TextureFilter.Linear);
If you are using texturepacker you can do this in one go by altering it's settings.
texturePackerSetting.filterMin = Texture.TextureFilter.Linear;
texturePackerSetting.filterMag = Texture.TextureFilter.Linear;
Or you could edit the atlas file itself by by changing the filter parameter to:
filter: Linear,Linear
This obviously costs more power since it needs to do more calculations for each pixel you drawn to the screen but I would not worry about this until your drawing is starting to get a bottleneck.
Another solutions is to draw pixel perfect which means you need to set your viewport to the size of the device gdx.graphics.getWidth, gdx.graphics.getHeight, in other words a ScreenViewport and draw your textures at exact sizes you want them. Of course this means a screen with more pixels sees more of your game world then a screen with less pixels and the more pixels a device has the smaller your textures will look. Another drawback of this is that you have to forget about any zooming or draw sprites for each level of zoom so they line up with the pixel grid of the device again.

Javafx center shape on screen inside Group

I made a sketch with the behavior I'm trying to get.
Sketch
So I want to display a rectangle in the middle of the screen and a triangle that covers part of the rectangle. The problem is, when I use a Stackpanethe rectangle is centered but the triangle as well and I can't move it to the bottom right position. When I use a Groupit is not centered. Is there any way to get my intended behavior?

Set alignment of your triangle. Use static setAlignment(Node child, Pos value) method:
StackPane.setAlignment(triangle, Pos.BOTTOM_RIGHT)

With Java's graphics shape drawing operations, is there an easy way to give the shapes transparency gradients and blurry edges?

What I would like is to give circles a fill color with a gradient that starts from the middle and then as it moves out to the edges becomes progressively more transparent, giving a blur effect. What is the simplest way of doing this?

Try setting an appropiately defined java.awt.RadialGradientPaint (using Colors with alpha), then render your circles using that. You may need to translate the graphics coordinate system to get the gradient centered in the circle. (http://docs.oracle.com/javase/7/docs/api/java/awt/RadialGradientPaint.html)
Or just make an image in a graphics program and simply draw the image.

Why do I need to disable GL_TEXTURE_2D after drawing string in order for shapes to render?

I'm using the Slick2D library in order to render text to the screen but in order to render gl shapes like Rect, I need to first disable GL_TEXTURE_2D. I'm just curious as to why that is needed. Why does GL_TEXTURE_2D disable the rendering of shapes?

The way OpenGL works is basically one large, global state machine. When you bind a texture, every triangle you draw afterwards will use that texture.
The issue here is that the text drawing doesn't unbind it's texture afterwards, so the shapes you draw afterwards will be using that texture instead of no texture. The reason why you think it's "disabling" rendering is because the texture is made up of characters with everything else being transparent. What you're seeing is OpenGL drawing your shape with opacity at 0.
What happens when you disable GL_TEXTURE_2D is that the texture gets unbound and you draw regularly without a texture.

Because the string's texture is applied. As you probably don't set any texture coords it probably uses a section of the texture that is transparent and hence you see nothing.