# Issue with alpha in P2D Renderer
**URL:** https://discourse.processing.org/t/issue-with-alpha-in-p2d-renderer/43137
**Category:** Coding Questions
**Created:** [November 3, 2023, 6:02pm UTC](https://discourse.processing.org/t/issue-with-alpha-in-p2d-renderer/43137 "2023-11-03T18:02:55Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@eltrem](https://discourse.processing.org/u/eltrem)
#### Post date: [November 3, 2023, 6:02pm UTC](https://discourse.processing.org/t/issue-with-alpha-in-p2d-renderer/43137/1 "2023-11-03T18:02:55Z")
Hello Processing Community,
I’ve encountered a challenging issue while working with the P2D renderer in Processing, specifically when trying to layer semi-transparent shapes over a white background. The expected result is a lighter color where the semi-transparent shape overlays the background. However, the actual result is a greyish shape, suggesting an issue with how alpha blending is being handled in P2D (probably related to pre-multiplication?)
Here’s the minimal code that reproduces the problem:
```auto
PGraphics backgroundLayer;
PGraphics shapeLayer;
void setup() {
size(400, 400, P2D);
// Initialize the background layer with white opaque background
backgroundLayer = createGraphics(width, height, P2D);
backgroundLayer.beginDraw();
backgroundLayer.background(255);
backgroundLayer.endDraw();
// Initialize the shape layer with a transparent background
shapeLayer = createGraphics(width, height, P2D);
shapeLayer.beginDraw();
shapeLayer.clear();
shapeLayer.endDraw();
}
void draw() {
// Draw a semi-transparent rectangle on the shape layer
shapeLayer.beginDraw();
shapeLayer.clear(); // Clear previous frame
shapeLayer.fill(255, 127); // Set color to white with half opacity
shapeLayer.noStroke();
shapeLayer.rectMode(CENTER);
shapeLayer.rect(width/2, height/2, width/2, height/2);
shapeLayer.endDraw();
// Draw the background layer
image(backgroundLayer, 0, 0);
// Set the blend mode for drawing the shape layer
blendMode(BLEND);
// Draw the shape layer
image(shapeLayer, 0, 0);
}
```
Here are the steps and attempts I have made to resolve this issue:
1. Explicitly setting the blend mode to `BLEND` before drawing the shape layer.
2. Clearing the shape layer with `clear()` to ensure no residual pixels from the previous frame.
3. Using the default renderer, which resolved the issue but is not compatible with the Syphon library that I intend to use.
The goal is to work with the Syphon library, which requires P2D, and thus finding a solution with P2D is imperative.
I’m reaching out for help to understand if there’s something I’m missing or if there’s a known workaround for this issue. Any insight, suggestions, or guidance would be greatly appreciated.
Thank you for your time and assistance!
---
### Author:  [@neilcsmith](https://discourse.processing.org/u/neilcsmith)
#### Post date: [November 8, 2023, 2:49pm UTC](https://discourse.processing.org/t/issue-with-alpha-in-p2d-renderer/43137/2 "2023-11-08T14:49:45Z")
> [@eltrem](#):
>
> suggesting an issue with how alpha blending is being handled in P2D (probably related to pre-multiplication?)
Yes, it’s almost certainly this [Add support for pre-multiplied alpha · Issue #3391 · processing/processing · GitHub](https://github.com/processing/processing/issues/3391) Processing has been broken here for a long time!
---
### Author:  [@eltrem](https://discourse.processing.org/u/eltrem)
#### Post date: [November 17, 2023, 6:56pm UTC](https://discourse.processing.org/t/issue-with-alpha-in-p2d-renderer/43137/3 "2023-11-17T18:56:46Z")
oops… sad to see this issue has been unattended for so long…