I am working on a simple painting app using LibGDX, and I am having trouble getting it to "paint" properly with the setup I am using. The way I am trying to do this is to draw with sprites, and add these individual sprites into a background texture, using LibGDX's FBO commands, when it is appropriate.
The problem I am having is something relating to blending, in that when the sprites are added to this texture that I am building, any transparent pixels of the sprite that are on top of pixels that have been drawn to previous will be brightened up substantially, which obviously doesn't look very good. The following is what the result looks like, using a circle with a green>red gradient as the "brush". The top row is part of the background texture now, while the bottom one is still in its purely sprite drawn form.
http://i238.photobucket.com/albums/ff307/Muriako/hmm.png
Basically, the transparent areas of each sprite are brightening anything below them, and I need to make them completely transparent. I have messed around with many different blending mode combinations and couldn't find one that was any better. GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA for example did not have this problem, but instead the transparent pixels of each sprite seem to be lowered in alpha and even take on some of the color from the layer below, which seemed even more annoying.
I will be happy to post any code snippets on request, but my code has become a bit of mess since I started trying to fix these problems, so I would rather only put up the necessary bits as necessary.
What order are you drawing the sprites in? Alpha blending only works with respect to pixels already in the target, so you have to draw all alpha-containing things (and everything "behind" them) in Z order to get the right result. I'm using .glBlendFunc(GL10.GL_SRC_ALPHA, GL10.GL_ONE_MINUS_SRC_ALPHA);
Related
I am using pixel colour inspection to detect collisions. I know there are other ways to achieve this but this is my use case.
I draw a shape cloned from the main canvas on to a second canvas switching the fill and stroke colours to pur black. I then use getImageData() to get an array of pixel colours and inspect them - if I see black I have a collision with something.
However, some pixels are shades of grey because the second canvas is applying antialiasing to the shape. I want only black or transparent pixels.
How can I get the second canvas to be composed of either transparent or black only?
I have achieved this long in the past with Windows GDI via compositing/xor combinations etc. However, GDI did not always apply antialiasing. I guess the answer lies in globalCompositeOperation or filter but I cannot see what settings/filters or sequence to apply.
I appreciate I have not provided sample code but I am hoping that someone can throw me a bone and I'll work up a snippet here which might become a standard cut & paste for posterity from that.
I have a pretty strange behaviour with three.js when I try to load different textures for an environment cube map. Everything works fine till I try to test the same scene with larger textures. My camera is pretty much stable so I only have to change one side of the env cube to a large resolution texture as that will be the background of the scene which will be visible, the other 5 sides are small pngs - those are only visible in reflection.
There is no clear breaking point, what seems to usually work as an image for the env.cube is about 600x600px-ish, going any higher resulting in the scene loading completely black.
To make the scene look nice on most devices, I have to go up to a resolution around 1500x1500px (so not insanely large) for the background, and I have no idea why it breaks with a bigger image.
What I already tried/did:
image paths are fine, overwriting a working image to a larger version also breaks the scene.
I had no other idea what to try, maybe it has to do something with photoshop and its image encoding or something along those lines?
the scene contains:
a camera, a gltf model to test with and the environment cube. everything works perfect with small textures.
I already looked at the texture documentation of threejs and found nothing about what could cause this behaviour, I'm completely stuck.
I'm working on a simple drawing application. My line is constructed using polygons and things look good so far. I would like to add a transparency feature and I used glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA); for that reason. However, because my polys sometimes overlap, I get the ugly result shown in the picture (multiple layers of transparency). What I would like to get is the figure in the left(no overlapping because there is no transparency), with an overall transparency.
I guess I could do this by keeping the polys from overlaping, but that would be a overkill for this task I think. There should be a way to control them at drawing time, but being a beginner with OpenGL doesn't help.
I'm sorry, but the way transparency works does not allow you to do what you want without manually keeping the polygons from overlapping. The way that transparency works is that it takes the colour of the surface below it, and uses the blending function you specify in order to calculate the final colour of the pixel.
In your program you are drawing multiple polygons with alpha on top of each other. That means that their colours add up, giving the result you see.
I've never actually written a drawing application, but you could perhaps take a look at triangle strips to draw your lines. They allow you to extend the line point by point, and make sure the geometry won't overlap with itself.
I am using LibGDX for a small app project, and I need to somehow take a series of sprites and place them (or their pixels rather) into a Pixmap. The basic idea is to take random sprites that are generated through various means while the app is running, and, only at specific times, merge some of them onto a single background sprite.
I believe that most of this can be done easily, but the step of getting the sprite images into the Pixmap isn't quite so obvious to me. The sprites also have various transparent and semi-transparent pixels, so simply grabbing the color at each pixel while it is all on the same screen isn't really applicable either, as it obviously shouldn't take the background colors with it.
If there is a suitable alternative to this that would accomplish what I am looking for I would also love to hear it. Any help is highly appreciated.
I think you want to render your sprites to an off-screen buffer (called an "FBO" or FrameBuffer in libgdx) (blending them as they're added), and then render that offscreen buffer to the screen as a single draw call? If so, this question should help: libgdx SpriteBatch render to texture
This requires OpenGL ES 2.0, which will eliminate support for some older devices.
I am doing my iPhone graphics using OpenGL. In one of my projects, I need to use an image, which I need to use as a texture in OpenGL. The .png image is 512 * 512 in size, its background is transparent, and the image has a thick blue line in its center.
When I apply my image to a polygon in OpenGL, the texture appears as if the transparent part in the image is black and the thick blue line is seen as itself. In order to remove the black part, I used blending:
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
Then my black part of the texture in the polygon is removed. Now only the blue band is seen. Thus the problem is solved.
But I want to add many such images and make many objects in OpenGL. I am able to do that, but the frame rate is very low when I add more and more images to objects. But when I comment out blending, the frame rate is normal, but the images are not seen.
Since I do not have good fps, the graphics are a bit slow and I get a shaky effect.
So:
1) Is there any other method than blending to solve my problem?
2) How can I improve the frame rate of my OpenGL app? What all steps need to be taken in order to implement my graphics properly?
If you want to have transparent parts of an object, the only way is to blend to pixel data for the triangle with what is currently in the buffer (what you are currently doing). Normally, when using solid textures, the new pixel data for a triangle just overwrites what ever was in buffer (as long as it is closers, ie z-buffer). But with transparency, it has start looking at the transparency of that part of the texture, look at what is behind it, all the way back to something solid. Then has combine all of those over lapping layers of transparent stuff till you get the final image.
If all you are wanting your transparency for is something like a simple tree sprite, and removing the 'stuff' form the sides of the trunk etc. Then you may be better of providing more complex geometry that actually defines the shape of the trunk and thus not need to bother with transparency.
Sadly, I don't think there is much you can do to try to speed up your FPS, other then cut down the amount of transparency you are calculating. Maybe even adding some optimization that checks images to see if it can turn of alpha blending for this image or not. Depending on how much you are trying to push through, may save time in the long wrong.