Develop Reference

How do I make 2d- Flashlight effect in Processing 3

For reference the effect I'm going for is this:
I'm working in Processing 3, NOT p5.js.
I've looked around processing forums, but i can't find anything that works in the current version or doesn't use PGraphics and a mask which from what I've read can be expensive to use.
My current ideas and implementations have resulted to drawing shapes around the player and filling the gaps in with a circles with no fill that has a large stroke weight.
Does anyone know of any methods to easily and inexpensively draw a black background over everything except a small circular area?
If this is the wrong place to ask this question just send me on my way I guess, but please be nice. Thank you:)

You could create an image (or PGraphics) that consists of mostly black, with a transparent circle in it. This is called image masking or alpha compositing. Doing a Google image search for "alpha composite" returns a bunch of the images I'm talking about.
Anyway, after you have the image, it's just a matter of drawing it on top of your scene wherever the player is. You might also use the PImage#mask() function. More info can be found in the reference.

Line Flickers along Tiles in libGDX

I am making a simple platformer with a tile-based map. However, when the camera moves there is white flickering which I think occurs along the tile boundaries, but it is hard to tell because they flicker quickly.
What I have tried:
adding padding to my Tileset. I have 4px padding around each tile, so it's not image bleeding.
setting the TextureFilter to nearest. It was never on anything else, so Linear wasn't the culprit.
Casting the camera position to an int. While this doesn't fix the flickering it also makes my camera jerky, so this is the worst possible solution.
Setting config.useCPUSync to false and config.vSync to true. While I have set vSync to true I can't set CPUSync to false because, as far as I am aware, this is no longer an option. I get a compile time error when I try.
I am just displaying the map by calling TiledMapRendere.render(), so I don't know if the padding from my Tileset or my Nearest TextureFilter are actually being applied correctly, but that is the only possible issue in my rendering process I can think of.
Any other ideas?
Edit:
So I tried rendering manually and I learned a few things.
Even if I cast every coordinate for each tile to an int and every coordinate in the camera, there is still flickering, so that is defiantly not the answer. However, I then set the TextureFilter on each tile to Linear and that DID solve the flickering, but I don't like how the textures look so it's not really a solution.

This took me forever to figure out: everywhere else I looked gave the solutions I tried above.
What I eventually did is extruded the outer pixels by 1 the same way I would have if I expected there to be blur. I think this worked because when the tiles were scaled, the application sometimes had to choose whether to use the outer pixel or a transparent pixel (my margins) and chose a transparent pixel. So now, the margin around each tile is just another pixel of the same color, so if it chooses that pixel it looks the same to us.

Drawing liquid with LibGDX

I'm quite new to LibGDX and OpenGL, but I managed to make a simple liquid simulation using Box2D API. See this link (this is someone's else animation):
Physics Liquid
Currently I render the liquid particles as circles just like in the first image, but I want to make it look more natural like on the third one.
The answer might be to use distance field and I tried this approach, but with no effect. I'm drawing each particle as a texture using SpriteBatch class, but that can be changed. I made a texture (from a procedural Pixmap) that represents each particle as a filled circle, with alpha channel decreasing further from the center, so the effect is similar to the second picture.
Now, I must enable a threshold filter to alpha channel, something like: "draw only pixels with alpha > 0.5". This is post-processing step, because it matters what is the alpha channel of a pixel after all particles have been draw. Might or might not be done with shaders (ProgramShader), but after some research I still have no clue how to do this. Thanks for ANY help.
EDIT: this example explains the method, but it's implemented in ActionScript.

This can easily be done using shaders, but funny thing is that you don't need to write them.
"draw only pixels with alpha > 0.5" is also used while rendering distance field fonts (fonts which look good even when scaled up).
Follow this link : https://github.com/libgdx/libgdx/wiki/Distance-field-fonts
Directly jump to the last step.
You should find exactly what you want.
Hope this helps.

Getting alpha channel/opacity working for lighting

I have two pixel arrays, foreground and lighting. When I draw a white radial gradient (blurry circle) onto the lighting array, I want it to make the foreground visible - much like a torch in terraria/starbound. However, I also want to be able to mix different colors of lighting, rather than be stuck with black to white.
So how do I manipulate the pixel arrays so that they 'multiply' (I believe it's called)? Or is there an easier way using RGBA which I have not been able to get to work (flickering black on white or image getting ever more posterized)?
So far most responses regarding alpha channels / opacity have been using libraries from java which for this project I want to refrain from using.
Any help much appreciated!

If you want to know how the blending modes (such as "multiply") work in image editing programs on the pixel-value level, read this: How does photoshop blend two images together?.
Note that if you want to make the image lighter, you need a mode like "screen", because "multiply" makes it darker.

Using a semi transparent texture to "mask" out a part of the background

I am attempting to create a "hole in the fog" effect. I have a background grid image, overlapped onto that I have a "fog" texture that I use to show that certain areas are not in view. I am attempting to cut a chunk out of "fog" that will show the area that is currently in view. I am trying to "mask" a part of the fog off the screen.
I made some images to help explain what I am after:
Background:
"Mask Image" (The full transparency has to be on the inside and not the outer rim for what I am going to use it for):
Fog (Sorry, hard to see.. Mostly Transparent):
What I want as a final Product:
I have tried:
Stencil-Buffer: I got this fully working except for one fact... I wasn't able to figure out how to retain the fading transparency of the "mask" image.
glBlendFunc: I have tried many different version of the parameters and many other methods with it (glColorMask, glBlendEquation, glBlendFuncSeparate) I started by using some parameter that I found on this website: here. I used the "glBlendFunc(GL_ZERO, GL_ONE_MINUS_SRC_ALPHA);" as this seemed to be what I was looking for but... This is what ended up happening as a result: (Its hard to tell what is happening here but... There is fog covering the grid in the background. Though, the mask is just ending up as an fully opaque black blob when its supposed to be a transparent part in the fog.
Some previous code:
glEnable(GL_BLEND); // This is not really called here... It is called on the init function of the program as it is needed all the way through the rendering cycle.
renderFogTexture(delta, 0.55f); // This renders the fog texture over the background the 0.55f is the transparency of the image.
glBlendFunc(GL_ZERO, GL11.GL_ONE_MINUS_SRC_ALPHA); // This is the one I tried from one of the many website I have been to today.
renderFogCircles(delta); // This just draws one (or more) of the mask images to remove the fog in key places.
(I would have posted more code but after I tried many things I started removing some old code as it was getting very cluttered (I "backed them up" in block comments))

This is doable, provided that you're not doing anything with the alpha of the framebuffer currently.
Step 1: Make sure that the alpha of the framebuffer is cleared to zero. So your glClearColor call needs to set the alpha to zero. Then call glClear as normal.
Step 2: Draw the mask image before you draw the "fog". As Tim said, once you blend with your fog, you can't undo that. So you need the mask data there first.
However, you also need to render the mask specially. You only want the mask to modify the framebuffer's alpha. You don't want it to mess with the RGB color. To do that, use this function: glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_TRUE). This turns off writes to the RGB part of the color; thus, only the alpha will be modified.
Your mask texture seems to have zero where it is visible and one where it isn't. However, the algorithm needs the opposite, so you should either fix your texture or use a glTexEnv mode that will effectively flip the alpha.
After this step, your framebuffer should have an alpha of 0 where we want to see the fog, and an alpha of 1 where we don't.
Also, don't forget to undo the glColorMask call after rendering the mask. You need to get those colors back.
Step 3: Render the fog. That's easy enough; to make the masking work, you need a special blend mode. Like this one:
glEnable(GL_BLEND);
glBlendEquation(GL_FUNC_ADD);
glBlendFuncSeparate(GL_ONE_MINUS_DST_ALPHA, GL_DST_ALPHA, GL_ZERO, GL_ONE);
The separation between the RGB and A blend portions is important. You don't want to change the framebuffer's alpha (just in case you want to render more than one layer of fog).
And you're done.

The approach you're currently taking will not work, as once you draw the fog over the whole screen, there's no way to 'erase' it.
If you're using fixed pipeline:
You can use multitexturing (glTexEnv) with fixed pipeline to combine the fog and circle textures in a single pass. This function is probably kind of confusing if you haven't used it before, you'll probably have to spend some time studying the man page. You'll do something like bind fog to glActiveTexture 0, and mask to glActiveTexture 1, enable multitexturing, and then combine them with glTexEnv. I don't remember exactly the right parameters for this.
If you're using shaders:
Use a multitexturing shader where you multiply the fog alpha with the circle texture (to zero out the alpha in the circle region), and then blend this combined texture into the background in a single pass. This is probably a more conceptually easy approach, but not sure if you're using shaders.
I'm not sure there's a way you can do this where you draw the fog and the mask in separate passes, as they both have their own alpha values, it will be difficult to combine them to get the right color result.