I'd like to blink out a texture in an android live wallpaper. I can easily just not draw that shape for a second, but I'd like it to look more realistic.
How can I blink (like an eye blink) a shape. I'd like it to progressively close. One idea was to have another duplicate shape with a fragment shader that only covered a percentage of the shape on each iteration of draw, but I'm not sure how to determine if the pixel should be transparent or not from within the shader. Any ideas?
Or is there a better way to accomplish this?
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I want to achieve the result like in the image below:
I assume, solutiuon is:
Cut the custom shape.
Scale received shape.
Apply blur to main texture.
Draw the shape on top.
Draw the real transparent drop on the top of shape.
My question is how to cut the texture in drop shape using vertex and/or fragment shader? Appreciate any ideas and suggestions abot the way to go.
I have a 3d mesh, which is a terrain. This runs perfectly fine btw, but I want to have shapes moving accross this terrain. These shapes are flat on the landscape and are blob-like: They can change shape and should follow the contoures and the heightmap of the terrain. These shapes can be painted on the landscape or flow over it, that doesn't matter.
The shapes are meant to be blocks of armies moving across the map, and this should be happening Real-Time! Also: they are 2d convex hull shapes. Also they are just one color with an alpha value (like blue with alpha 0.25f).
The only problem is: I can't figure out how to do this and the question is: Can anyone tell me how to do it?
My first thoughts were just to copy the terrain vertex matrix, push it up a bit so it will be on top of the terrain, load this buffer into a VBO and update the index buffer according to the position and shape needed and then draw the shape. This is rather slow and inefficient, especially when the shape is moving and changing. Also, the resolution of the heightmap is 175x175, so the movement is not at all smooth but rather jaggy.
Then I thought, but rather new to this area, update the shape outlines to the fragment shader of the terrain and let the shader decide if a point lies in that area and change color accordingly. This also was a really slow option, but if anyone sees potential and a good way to do this, tell me!
The next option was to draw directly onto the texture, which is still in the failing stage. If someone has any good ideas on how to draw a scene to a flat area and then put that on a terrain mesh, that would be great!
So if anyone has a solution to draw a shape (or multiple) on a terrain? That would be awesome. Thanks in advance!
Using OpenGL ES, there seem to be two viable options for rounded rectangles:
Manually draw the shape using trig. (This is what I'm currently doing.)
Use a a texture or group of textures that scale appropriately, such as 9-Slice Scaling
The problem with the first option is that antialiasing does not come for free, and if you are aiming for compatibility with a wide array of devices, one can't count on OpenGL antialiasing hints to actually work on the hardware. So you're left with choppy-looking rounded rectangles, especially for small ones, and the performance overhead of making another vertex array draw call. I would like to switch away from this
The second option (9-Slice or 9-Patch) seems to be the go-to method for UI rounded rect elements, but there is surprisingly little information out there about implementing 9-patching in OpenGL ES.
What I would like is: an efficient strategy for rendering antialiased rounded rectangles in OpenGL ES with adjustable border widths, border colors and fill colors. Any suggestions?
What you want is essentially a technique called Edge Anti-Aliasing.
It is described very well in this answer: OpenGL ES iPhone - drawing anti aliased lines
Just apply the transparent vertexes at outmost borderline of your rectangle.
This is my first question...
I've a square (triangle strip) with a texture (.png).
This .png have smooth corners like a play card.
The four extremities (corners) are transparent.
When draw the square, in the corners, i see the white color of the shape.
(Like a background behind the texture)
My question is:
How can i draw a transparent color for the shape, but mantain the color of the texture with a full apha?
(If i set transparent colors.... then also the texture become transparent)
How can i separate the two contexts?
Thanks in advance.. and sorry for my bad english.
First of all, you must use a texture format with alpha channel.
Then if you are using fixed function pipeline, you must enable blending.
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glEnable(GL_BLEND);
If you are not using fixed function pipeline, please share the fragment shader code; and a little more details on how you are using it.
I'm trying to create a particular effect where I have a bunch of particles on the screen which leave trails that slowly fade. I was hoping that I could simply use glClear with a small alpha value to do this but that doesn't seem to be working.
My second idea was to draw a black face on the front of the screen but this doesn't seem to be giving me the right effect, the particles are faded but the background doesn't really fade. My next idea is to render to a texture and fade that texture but that's a lot of extra work and I'm not sure if it will solve my problem. Can anyone think of a way to do this? Am I missing something?
Edit Also I'm having trouble finding information about rendering to a texture on android. If anyone has some links to articles that would be great.
Assuming that your 'particles' ar just a bunch of textured sprites, you can simply add color data for each vertex of the sprite using glVertexPointer(). The color you set for the vertices will then be blended with the texture of the sprite. You can easily update these values to achieve a 'fading' effect.
E.g. if you set RGBA = (1,1,1,1) for each vertex, the sprite will appear as before (no translucency), set RGBA = (1,0,0,1) the sprite will appear red (no translucency), set RGBA = (0.5,0.5,0.5,0.5) the sprite will appear half translucent, etc. You will have to set the correct glBlendFunc() beforehand to get the desired behaviour!
Cheers, Aert.