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I know there is a lot of threads about that, but no one have a working example anymore, so again question: how to draw a "glow" effect using lwjgl and slick around simple shapes, like this circle?


see: http://stackoverflow.com/questions/1037 ... ck-in-them


I know i must use GL functions to achieve this, but with no working code it's hard to understand the process.

Thanks in advance

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The easiest and most efficient way to do this is to bake the glow into your sprites (e.g. using Photoshop).

If you need the glow to be dynamic, then another common technique is to use a two-pass blur shader. This requires the following OpenGL extensions:
- GL_ARB_shader_objects or GL20
- GL_EXT_framebuffer_object or GL30

Easy way of doing it:

1. Render your scene or "glow objects" to texture A
2. Bind texture A, then using the horizontal shader, render a quad to texture B
3. Bind texture B, then using the vertical shader, render a quad to texture A

The textures you're rendering to should be bigger than the image (otherwise the blur will be cut off abruptly), or simply the size of the screen for simplicity's sake. You should optimize this by only applying the effect to texture A when necessary (i.e. when glow needs updating).

The dev branch includes a ShaderProgram utility as well as two shader tests. ShaderTest is a simple invert shader (might help you get started with shaders). ShaderTestAdvanced is a blur shader, basically what is described above. It's a bit hackish, and needs a little cleaning up, but it should get you started.

I've tried to build Share with slick but without any luck, can you provide a "hello world" eclipse project about that? So I can work on it

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"Hello world" on pulling source code? Sure, if I have some time I'll write a little tutorial for the wiki.

thanks!

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Where is this "dev branch"?

I've been trying to find a Slick Shader tutorial for many months now.

How to apply a shader to a specific image/texture only, and not to the whole scene?
I found a tutorial for render-to-texture ( Here ), but as far as I understand the ShaderTest.java in the newest build applies the shader to the whole screen.

Also, how to render it so that stuff behind and in front of the shader-texture won't get affected by the shader in any way?

EDIT
Okay, it seems to work just the way I wanted, not the way how I initially thought.
The shader is not applied to the whole scene, but rather only to those images that are drawn between the lines
program.bind();
and
program.unbind();

If I'm wrong please explain how it actually works.

EDIT 2

A shader test:

Looks cool!

When a shader is bound, anything rendered will use that shader. So if you've got an invert colour shader (returning 1.0 - RGB) and you draw a white rectangle with g.drawRect, it will appear black as a result. Same goes for fonts and images.

The reason we blur the whole screen in the demo: if we only blurred the image, it would get abruptly cut off where the blur meets the edge of the image. To remove this, we need to blur a larger area than the image's bounds -- i.e. the full screen. In order to affect the whole screen with a shader, you need to first render everything as per usual into an image, and then bind your shader and render that "full screen image" onto the screen (thus making the shader affect the full screen image).

If you've got more questions, just ask.