Bump only the reflections of a shader

[seandunderdale]

Is it possible to only have the bump map affect only the reflections of a shader? Im trying to make car window glass reflections have the warped effect by bumping the reflections but the refraction gets distorted too (it might be technically correct as some photo refrerence does show warped refractions). I have broken the layers of glass out into a blend shader and added a bump map to the reflection layer of that, which does kind of solve the problem. I get control over the glass window reflection distortion, and I get clean refractions. This setup breaksdown though since I need "reflect on backside" turned on to get the visual relationship of the glass and the window frit band correct, so the reflection and refraction need to be done with one shader.

[fixeighted]

Unsure of the solution to this but!..... I never knew those little dots were called a 'frit band', nor knew what their purpose was, so
thanks for providing my morning educational snippet.

[kosso_olli]

Is it possible to only have the bump map affect only the reflections of a shader? Im trying to make car window glass reflections have the warped effect by bumping the reflections but the refraction gets distorted too (it might be technically correct as some photo refrerence does show warped refractions). I have broken the layers of glass out into a blend shader and added a bump map to the reflection layer of that, which does kind of solve the problem. I get control over the glass window reflection distortion, and I get clean refractions. This setup breaksdown though since I need "reflect on backside" turned on to get the visual relationship of the glass and the window frit band correct, so the reflection and refraction need to be done with one shader.

Technically, the frit band does not have any reflection whatsoever, because it is printed to the backside of the glass. The reflections you see on the frit band are the reflections of the glass on it's backside, as you say. You might get away with copying all the reflection properties to the frit band (in a blend shader, that's how we do it), and then disabling the reflect on back side for the glass.

[seandunderdale]

Totally agree...one of my bugbears is the frit having reflection or grey tone in it. Ive had some heated conversations in studios about this. What I find though is that when the frit geo is fully below the window glass geo, you dont get it showing up visible in the render. I move it up so it sits inside the window geo, which has thickness, but then I also need the windscreen glass to have "reflect on backside" on to get the desired results. I assume its because glass does reflect internally in real life, and the frit is black, so the glass ends up with this extra reflection effect / amount, which is what causes the glass and frit separation visually in render. This whole effect is broken when I make a blend shader glass setup, which is the only way I can bump the glass reflection to get the glass warping, and keep the refraction clean.

Ill try your method and see how it goes. I do feel like a cheat / hack will be the solution.

[matthew999]

How's about Turn off refraction for glass as it's a constant thickness anyway. Have frit as solid black and glass single sided.

[seandunderdale]

Ive found I can get the results I need by turning off reflections and turning on coat. I use the bump map in the coat, and also turn on "reflect on backside". This gives me a clean refraction with no bump, also the window ceramic and glass separation, and also the control over the glass bump distortion amount. Let me know if anyone sees any issues with using coat as the glass reflection instead of the actual reflection. I didnt actually think it would work since I wasnt sure reflect on backside would work with the coat layer.