The texture I'm using is doing filtering for the edges but it creates gaps for the extrusion.
In the photo
The yellow shape is the texture, the white shape is an extrusion and the red shape is the background.
The red background should not be seen between the face, the yellow shape, and the extrusion.
What approach should I use?
Related
I want to use openGL to draw a hollow sphere. The material properties of sphere is different for front and back surfaces. Now I want to mask the sphere with a text, so that the inner surface becomes visible from the text area. I am not able to understand how to achieve it.
Draw the sphere twice:
glCullFace(GL_FRONT), then draw sphere. This will put all back-facing triangles in the depth and color buffers.
glCullFace(GL_BACK), bind text texture, enable alpha test, draw sphere. Where the alpha test fails the color buffer won't be updated and you'll be able to "see through" to the inside of the sphere.
I am using opengl and c++ doing image processing. The idea is simple, I will load an image, draw a polygon by clicking and then apply an effect (desaturation for instance) only to the pixels in the interior of the polygon shape just created.
Can anyone give me any direction on how to limit the effect to the pixels within the interior of the polygon? Loading the image and drawing the polygon is not a problem
Supposing the following situation :
The picture on which you want to apply the effect takes the whole screen
The picture is rendered using opengl , probably through a simple shader, with the picture passed as a texture
You can do the following approach :
consider the screen as being a big texture
you draw a polygon, which will be rendered on top of the rendered texture
inside the polygon's vertices insert the uv's coresponding to the 2D coordinates on the screen (so from screen space to uv space (0 , 1 ) )
draw the picture normaly
on top of the picture draw your polygon using the same picture as texture, but with a different shader
So instead of trying to desaturate a specific region from your picture, create a polygon on top of that region with the same picture, and desaturate that new polygon.
This would help you in avoiding the stencil buffer.
Another approach would be to create the polygon, but draw it only on the stencil buffer, before the picture is drawn.
If you draw a sphere using an impostor based ray-tracing approach as described for example here
http://www.arcsynthesis.org/gltut/Illumination/Tutorial%2013.html
you typically draw a quad and then use 'discard' to skip pixels that have a distance from the quad center larger than the sphere radius.
When you turn on anti-aliasing, GLSL will anti-alias the border of the primitive you draw - in this case the quad - but not the border between the drawn and discarded pixels.
I have attached two screen shots displaying the sphere and a blow-up of its border. Except for the top-most pixels, that lie on the quad border, clearly the sphere border has not been anti-aliased.
Is there any trick I can use to make the impostor spheres have a nice anti-aliased border?
Best regard,
Mads
Instead of just discarding the pixel, set your sphere to have inner and outer radius.
Everything inside the inner radius is fully opaque, everything outside the outer radius is discarded, and anything in between is linearly interpolated between 0 and 1 alpha values.
float alpha = (position - inner) / (outer - inner);
Kneejerk reaction would be to multisample for yourself: render to a texture that is e.g. four times as large as your actual output, then ensure you generate mip maps and render from that texture back onto your screen.
Alternatively do that directly in your shader and let OpenGL continue worrying about geometry edges: sample four rays per pixel and average them.
So I have no idea how I should be doing what I want do so I'll explain as best as I can.
http://i.stack.imgur.com/j65H8.jpg
So imagine that entire image is a 2d square 128x128 and each color I want to apply a texture to that part of the 2d square. Also I want it to stretch as well so Red, Aqua, Green and Purple never stretch in any direction but Pink stretches all directions and then Grey, Yellow, Black and Orange stretch in the longest direction (grey/orange = width expands, yellow/black = height expands). When stretched it should look like this:
http://i.stack.imgur.com/wJiKv.jpg
Also I am using C++.
so I have a problem with the alpha value in my texture. Basically the pixmap is set all black then I drew a filled circle with the alpha value set to 0 in order for the area of the circle it to be transparent (yes I set blending to none), then I created the texture out of the pixmap like this:
Texture myTexture = new Pixmap(TransparentCirclePixmap); // this constructor takes a pixmap
if I draw this texture the circle is not transparent it has a color that is not the background in my game.
so basically what i want is to draw a transparent circle in my pixmap and create a texture from that pixmap and when I draw the texture to the screen the interior of the circle displays whatever was in the background of my game.