Hi,

I was studying making bloom/glow effect in OpenGL and following the tutorials from learnopengl.com and ThinMatrix (youtube) tutorials, but i am still confuse 

on how to generate the bright colored texture to be used for blur.

Do I need to put lights in the area of location i want the glow to happen so it will be brighter than other object in the scene?, that means i need to draw the scene with the light first?

or does the brightness can be extracted based on how the color of the model was rendered/textured thru a formula or something?

I have a scene that looks like this that i want to glow the crystal

can somebody enlighten me on how or what the correct approach is?

really appreciated!

I would guess the crystal is done with a simple emissive property, and a point light without shadowmap?

Bloom is typically done by extracting the bright pixels of the scene, then doing a blur, then additively applying the blurred pixels back onto the frame buffer.

The bright pixels can come from bright lighting or bright emissive values. What you determine to be "bright" or "bloomable" is up to you.

Hi,

Bloom, Glow  and Blur effects whether in HLSL or GLSL are normally done using post processing effect, post processing meaning you do the filtering after you render the scene to a render target usually bloom and blur effects are combined together to get a better result.

1. Render your regular scene to a render target
2. On your BloomBlur effect pass the render target as sampler for lookup table for brightness
   and do the necessary brightness,blur  adjustment to the final sampler ( other sampler )
3. Draw the final sampler on screen

I've one this in the past, the que to look for is "Bloom Post processing effect",  information about this is abundant over the internet even with effects sample.