# Is it possible to change the transparency of a PShape object in draw()?

**URL:** <https://discourse.processing.org/t/is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429>\
**Category:** Processing.py\
**Created:** [July 2, 2018, 10:20am UTC](https://discourse.processing.org/t/is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429 "2018-07-02T10:20:56Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![solub](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/solub/32/333_2.png) [@solub](https://discourse.processing.org/u/solub)\
**Post date:** [July 2, 2018, 10:20am UTC](https://discourse.processing.org/t/is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429/1 "2018-07-02T10:20:56Z")

</div>

Hi,

The title says it all, I’d like to change in `draw()` the `alpha` value of a PShape object originally created in `setup()`.

A quick example:

```auto
def setup():
    size(800, 800, P3D)
    global shp
    
    shp = createShape()
    shp.beginShape(POINTS)
    shp.strokeWeight(15)
    for e in range(300):
        shp.stroke(random(255), random(255), random(255))
        shp.vertex(random(width), random(height), random(width))
    shp.endShape()
                   
def draw():
    background(0)
    
    shape(shp, 0, 0)

```

I know I can change the visibility of the shape after it’s created with the `setStroke()` method but can’t find an equivalent for the `alpha` value.

I could certainly combine `setStroke()` with `color()`…

```auto
def draw():

alpha_value = 110
shp.setStroke(color(255, alpha_value))

shape(shp, 0, 0)

```

… but then I’m losing all the colors previously set in setup().

How can I change the transparency while preserving all the colors ? Is that even possible ?

Would love your help,

Thank you

---

<div class="post-metadata">

**Author:** ![GoToLoop](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/gotoloop/32/86_2.png) [@GoToLoop](https://discourse.processing.org/u/GoToLoop)\
**Post date:** [July 2, 2018, 12:49pm UTC](https://discourse.processing.org/t/is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429/2 "2018-07-02T12:49:47Z")

</div>

Here’s my attempt, for both Java & Python modes: 🤠

```auto
/**
 * PShape Change Alpha Color (v1.0)
 * GoToLoop (2018/Jul/02)
 *
 * https://Discourse.Processing.org/t/
 * is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429/2
 */

static final int DOTS = 300, DIAM = 020, RAD = DIAM >> 1;
PShape shp;

void setup() {
  size(800, 600, P2D);
  smooth(8);
  noLoop();

  strokeWeight(DIAM);

  shp = createShape();
  shp.beginShape(POINTS);

  for (int w = width - RAD, h = height - RAD, i = 0; i < DOTS; ++i) {
    shp.stroke((color) random(PImage.ALPHA_MASK));
    shp.vertex(random(RAD, w), random(RAD, h));
  }

  shp.endShape();
}

void draw() {
  clear();
  shape(shp, 0, 0);
}

void mousePressed() {
  if (mouseButton == LEFT) for (int i = 0; i < DOTS; ++i) {
    final color stroke = shp.getStroke(i);
    final color rawStroke = stroke << 010 >>> 010;
    final color alpha = (color) random(0x100) << 030;
    final color alphaStroke = alpha | rawStroke;
    shp.setStroke(i, alphaStroke);
  } else if (mouseButton == RIGHT) for (int i = 0; i < DOTS; 
    shp.setStroke(i++, (color) random(PImage.ALPHA_MASK)));
  else for (int w = width - RAD, h = height - RAD, i = 0; i < DOTS; 
    shp.setVertex(i++, random(RAD, w), random(RAD, h)));

  redraw();
}

```

```auto
"""
 PShape Change Alpha Color (v1.0.3)
 GoToLoop (2018/Jul/02)

 https://Discourse.Processing.org/t/
 is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429/2
"""

ALL_COLORS = PImage.ALPHA_MASK
NO_ALPHA = ~PImage.ALPHA_MASK

DOTS = 300
RANGE = tuple(range(DOTS))

DIAM = 020
RAD = DIAM >> 1

def setup():
    size(800, 600, P2D)
    smooth(8)
    noLoop()

    strokeWeight(DIAM)

    global shp
    shp = createShape()
    w, h = width - RAD, height - RAD

    shp.beginShape(POINTS)

    for i in RANGE:
        shp.stroke(int(random(ALL_COLORS)))
        shp.vertex(random(RAD, w), random(RAD, h))

    shp.endShape()

def draw():
    clear()
    shape(shp, 0, 0)

def mousePressed():
    if mouseButton == LEFT:
        for i in RANGE:
            stroke = shp.getStroke(i)
            rawStroke = stroke & NO_ALPHA

            alpha = int(random(0x100)) << 030
            alphaStroke = alpha | rawStroke

            shp.setStroke(i, alphaStroke)

    elif mouseButton == RIGHT:
        for i in RANGE: shp.setStroke(i, int(random(ALL_COLORS)))

    else:
        w, h = width - RAD, height - RAD
        for i in RANGE: shp.setVertex(i, random(RAD, w), random(RAD, h))

    redraw()

```

---

<div class="post-metadata">

**Author:** ![WakeMeAtThree](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/wakemeatthree/32/38_2.png) [@WakeMeAtThree](https://discourse.processing.org/u/WakeMeAtThree)\
**Post date:** [July 2, 2018, 12:50pm UTC](https://discourse.processing.org/t/is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429/3 "2018-07-02T12:50:21Z")

</div>

Hi Solub! 🙂  
You can instantiate colors and points once in setup, and then call them later in draw

```python
a = 0
def setup():
    size(800, 800, P3D)
    global shp, colors, points
    
    #Initiate colors and points once
    colors = [color(random(255),random(255),random(255)) for i in range(300)]
    points = [PVector(random(width), random(height), random(width)) for i in range(300)]
    
    shp = createShape()
    shp.beginShape(POINTS)
    shp.strokeWeight(15)
    for i,j in zip(colors,points):
        shp.stroke(i)
        shp.vertex(j.x,j.y,j.z)
    shp.endShape()

                   
def draw():
    background(0)
    global a
    for i,j in enumerate(colors):
        shp.setStroke(i,color(j,int(255*sin(a))))

    shape(shp, 0, 0)
    
    a += 0.01;

```

Edited: Since they’re both stored in a list, you can keep ~~recreating the shape but~~ changing the alpha of the stroke everytime (i mapped a simple sin for a quick test).

~~Is this the most efficient way? I’m not sure, I was hoping that there is a setVertexColor method in the documentation, but couldn’t find any. I would prefer doing that than simply recreating the shape. Hope this helps.~~ Just by using setStroke(int index, color) method would be fine.

---

<div class="post-metadata">

**Author:** ![solub](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/solub/32/333_2.png) [@solub](https://discourse.processing.org/u/solub)\
**Post date:** [July 2, 2018, 4:17pm UTC](https://discourse.processing.org/t/is-it-possible-to-change-the-transparency-of-a-pshape-object-in-draw/1429/4 "2018-07-02T16:17:44Z")

</div>

@WakeMeAtThree @GoToLoop Thank you both of you for your replies !

Upon reading your solutions I realized my problem was a bit more complex than I first thought and my question should have been more precise.

I’m trying to highlight a _specific_ cluster within a point cloud by decreasing the alpha value of every points except the ones from the selected cluster.

However, not only the point cloud is a single PShape object (impossible to select a specific area) but also it is generated from a point shader (impossible to play with the alpha value without messing with the fragment shader directly)

Fortunately, thanks to your suggestions, I somewhat managed to find a workaround. The process goes like this:

**pointShader**

- creating an alpha variable

**setup** ()

- loading the pointShader and setting alpha to `0.5`
- create a single PShape from the different point clusters
- storing the colors in a 2D array list

**draw()**

- applying the point shader
- displaying the PShape (original point cloud with alpha set to 0.5)
- reseting the point shader (`resetShader(POINTS)`)
- redrawing the selected points over the points already displayed
- setting their colors from the 2D array list
- setting their alpha value to max (not mendatory, `255` by default)

The only issue I have is that when I reset the shader I’m losing the perspective effect for the new points.

So I end up with a whole point cloud with a perspective effect and a cluster where the point sizes don’t vary in space, no matter how far their are from the camera.

[https://giant.gfycat.com/SparklingSecondaryBlueshark.webm](https://giant.gfycat.com/SparklingSecondaryBlueshark.webm)

**point cloud with** `alpha = 1.0`  
[![](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/1X/ce546faab3c6bb755e3620a284525290395b2cae.png) ](https://i.imgur.com/Z7CCWMS.png)

**point cloud with** `alpha = .4`  
[![](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/1X/eb63cde9b43a1d473a4fa478bb1cd35b13ae3dd2.png) ](https://i.imgur.com/mdBuQkg.png)

You can see the new points. From a distance they look bigger than the original ones from the PShape.

**close up with** `alpha = 1.0`  
[![](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/1X/f5399a113652df8dcba6dfdb29794ec9b0bce7f5.png) ](https://i.imgur.com/EX1mt9x.png)

**close up with** `alpha = .4`  
[![](https://canada1.discourse-cdn.com/flex036/uploads/processingfoundation1/original/1X/512bf04e16574e04ff44ab37b786dc3a4d88eb59.png) ](https://i.imgur.com/2dueL0H.png)

But up close, it’s the contrary, they’re smaller than the original points. Hence, the difficulty to distinguish them from the other points.