I have a texture and I want to draw it to a FrameBufferObject. The texture has transparent areas. I would like the following:
For all transparent pixels, let them be drawn transparent in the FrameBufferObject.
For all non-transparent pixels, let them be drawn using a color of my choosing, ie pure red (ignore their actual rgb value)
I've tried Batch.setColor(red) before drawing the texture, but that just tints it - I want all non-transparent pixels to be drawn pure red.
I am also trying to figure out how to achieve this in just opengl directly, looks like there may be a way to do this with blending, which can then be related back to gdx.
Thanks
You need to write a shader and the shader is the OpenGL program that renders the texture. So your shader would render transparency without change and all else would the color of your own choosing.
The following link has libgdx shaders for palette swapping i.e. direct reassignment of color at render, which you can easily adapt for single color and transparency.
https://www.javaer101.com/en/article/12241616.html
Related
I would like to delete a portion of a texture defined by a black and white mask and replace it with the color of the adjacent pixels
this is an example to make you understand better
this is my try
first I draw the mask with the white area with the part of the image to be preserved and black with the portion to be obscured with
glDisable (GL_BLEND);
then I draw over the image with
glEnable (GL_BLEND);
glBlendFunc (GL_DST_COLOR, GL_ZERO);
in this way I can delete the part defined by the mask but I don't know how to fill it inside with the colors of the adjacent pixels
thx!
EDIT
I found this shadertoy that does exactly what i'm looking for
https://www.shadertoy.com/view/4ty3Dy
but I have to apply this to a video, and this shader seems to modify a static image multiple times by calling itself while the frames are running
I should have the effect generated for each frame in the simplest and lighter manner to run the shader on a rpi4
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'm using a prefab for a box shape, which has a front and back plane.
My images are PNG and have transparent areas around the edge. I dragged the image onto my front plane, which now has a drop-down box for "Shader".
First I chose Shader: "Standard" but the transparent areas of my PNG image weren't transparent, so in order to fix that I changed it to "Sprites / Diffuse"... now the image looks fine (from the front).
However, when I rotate the shape, the image is also visible from the back. I want a way to not see the image / texture from the back.
How can I make the images only visible from the front side of a plane, whilst also preserving the transparency areas of the image / texture?
If you are using the standard built-in shader, you need to set the rendering mode to transparent in order for the texture's alpha channel to be transparent. The sprite shader, by default, forces the rendering of otherwise invisible back-faces, whereas the standard shader does not.
Basically what I want to achieve is a sprite highlight animation effect as displayed below.
The idea is that the white-translucent gradient sprite moves on top of the other sprite (left-to-right), using a blend mode like Overlay (Photoshop). The difficult part is that the top gradient sprite should only be drawn on the visible pixels of the sprite underneath. The other part of the gradient overlay should be discarded to not affect the background or other sprites underneath (like on the image to the far right).
Is it possible to achieve that effect with a clever combination of OpenGL blend modes and how, or would I have to create a custom shader to combine these sprites?
Background: I'm using libgdx with OpenGL ES 2.0 and the app runs on Desktop, Android and iOS.
There arę many ways to do it. The simplest one:
You should render button and hilight in a single pass. In fragment shader, after sampling button texture and hilight texture calc the output color as for blending (could be mix(c1,c2,c2.a)) and alpha as button texture alpha only. Of course enable blending in usual way: (srcalpha,1-srcalpha)
Is it possible with OpenGL ES to texture a quad in such a way that all pixel (0,0,0) of the texture are not drawn while all the others are drawn? I have RGB888 images and the black color (0,0,0) is to be considered as completely transparent, while the other colors are completely opaque.
Thx
You could apply a fragment shader which sets the alpha color for pixels with RGB=(0,0,0) to 0. See here for details on writing a fragment shader.