I currently have a custom modifier built using `dr...

# compose-android

[Jonathan]

I currently have a custom modifier built using drawBehind { ... } to draw a custom shadow directly on a Canvas. I’m currently in the process of optimizing code and I wondered if I would get any performance benefits using a Modifier.graphicLayer { ... } or maybe even using the DrawModifierNode?
I’m curious to know if the Modifier.graphicLayer {} would potentially gain performance improvements because out-the-box Modifier.shadow(...) uses a graphicLayer to achieve a shadow. Any thoughts, recommendations or links to articles that would help me make a good decision.

[romainguy]

The default implementation uses a graphicsLayer because it has to. Material shadows are handled at the RenderNode level, which is what a graphicsLayer creates by default

[romainguy]

You’d use a graphicsLayer in one of two situations:

[romainguy]

• If re-issuing all the draw calls is expensive or if you want to apply common transforms cheaply to all those draw calls (rotation for instance) without having to re-record them

[romainguy]

• If rasterizing all the draw calls is expensive, you would use an offscreen graphicsLayer (which is effectively a GPU texture). This should rarely be needed, but it sometimes is for certain effects (blend modes) or correctness (stacked alpha)

[Jonathan]

My current modifier accepts an offset to customize the shadow spread, a Shape and a Color .
Inside of my drawIntoCanvas block I assign the provided Color on the Canvas’ paint object and set anti alias to true, then I grab the outline of the specified Shape and draw it on the Canvas. Does using a graphicLayer seem like a misuse? The shadow will need alpha blending because some content with a Modifier will be drawn on top of a custom background that we’d like to still be visible.

[romainguy]

A graphicsLayer seems unnecessary for what you are doing. Alpha blending is fine; alpha becomes a problem when you want to apply alpha to multiple overlapping primitives. It’s not the same drawing a 50% transparent blue rectangle and then a 50% transparent red rectangle that overlaps the blue rectangle, vs drawing the two rectangles 100% opaque and making the result 50% transparent

[Jonathan]

Gotcha! Would you recommend to use a DrawModifierNode or just replace my drawBehind {} with a drawWithCache {} ?