Changing vertex() color within beginShape()

Programming Questions

jaytex

Changing vertex() color within beginShape()

in Programming Questions • 1 year ago

I want to vary the colour of the line along it's length. My code below produces lines with uniform colour. I assume it just uses the colour resulting from the first stroke().

Any way to do this with standard Processing rendering (apart from splitting into different shapes, which is too inefficient)?

noFill();
strokeWeight(1.f);
beginShape();
for(PVector pv : points) // Points is a LinkedList<PVector>.
{
stroke(random(1.f) * 255, random(1.f) * 255, random(1.f) * 255, 255);
vertex(pv.x, pv.y);
}
endShape();

Replies(10)

tfguy44

Re: Changing vertex() color within beginShape()

1 year ago

// You may need to re-work it...
size(400, 400);
background(0);
noFill();
strokeWeight(1);
stroke(255);
translate( 0, 200);
line( 0, -200, 0, 200);
line( 0, 0, 400, 0);
int x;
// Try 1. Hrm.
//beginShape();
//for ( x = 0; x < 400; x++ ) {
// vertex( x, 180*sin(map(x, 0, 400, 0, TWO_PI)) );
// stroke(random(255), random(255), random(255));
//}
//endShape();
// Try 2.
for ( x = 1; x < 400; x++ ) {
beginShape();
stroke(random(255), random(255), random(255));
vertex( x-1, 180*sin(map(x-1, 0, 400, 0, TWO_PI)) );
vertex( x, 180*sin(map(x, 0, 400, 0, TWO_PI)) );
endShape();
}

jaytex

Re: Changing vertex() color within beginShape()

1 year ago

Thanks.

Try 1 replicates my problem.

Try 2 "works", but as I said in the original question I want to avoid splitting it into different shapes. This is for a) efficiency reasons and b) because I really want to use curveVertex(), and splitting into different shapes will break the curve.

Ale_

Re: Changing vertex() color within beginShape()

1 year ago

Hi Jay, you simply have to use P3D rendering mode.

Regards!

Ale · http://60rpm.tv/i

jaytex

Re: Changing vertex() color within beginShape()

1 year ago

Thanks Ale_, unfortunately I need to use the PDF renderer.

Jesse Sco..

Re: Re: Changing vertex() color within beginShape()

1 year ago

Sorry, off topic, but I've never gotten that... do you have to setup your whole sketch to use PDF, or can you just not set either it or DXF when you call beginRecord() ??

tfguy44

Re: Changing vertex() color within beginShape()

1 year ago

You should still be able to rework it without having to change much. Like so:

boolean isFirstTime = true;
float lastX, lastY;
for(PVector pv : points) // Points is a LinkedList<PVector>.
{
if( isFirstTime ){
isFirstTime = false;
} else {
stroke(random(1.f) * 255, random(1.f) * 255, random(1.f) * 255, 255);
beginShape();
vertex( lastX, lastY);
vertex(pv.x, pv.y);
endShape();
}
lastX = pv.x;
lastY = pv.y;
}

You'll have to tidy that up, but it should be what you want.

jaytex

Re: Changing vertex() color within beginShape()

1 year ago

Thanks tfguy, but again your solution is using repeated begin/endShape() calls.

As I said, this will not work for what I'm trying to do. It must be a single shape, since I want to use curveVertex(), and it is also inefficient.

jaytex

Re: Changing vertex() color within beginShape()

1 year ago

Just found this in the comment for beginShape(int) in PGraphics.java (emphasis mine):

The P3D renderer settings allow stroke() and fill() settings to be altered per-vertex, however the default P2D renderer does not. Settings such as strokeWeight(), strokeCap(), and strokeJoin() cannot be changed while inside a beginShape()/endShape() block with any renderer.

This confirms what Ale_ said. I've confirmed in my tests that the PDF renderer has the same limitation as the P2D renderer w.r.t. changing vertex colour per-vertex.

I'm digging into the source to see if there is a workaround.

Update:

PGraphicsPDF extends PGraphicsJava2D

This explains why the PDF renderer also doesn't support per-vertex colour. After looking into the PGraphics2D source, it appears there isn't a straightforward workaround. I'm going to try rendering to PDF directly via the iText Library, which is what PGraphicsPDF uses.

jaytex

Re: Changing vertex() color within beginShape()

1 year ago

Just an update with what I found. To restate what I was trying to do: I needed to render to P2D and PDF with per-vertex linear color interpolation along lines and curves (just your standard color lerp rasterisation like what you get with OpenGL (P3D) or D3D).

I can confirm that Java2D itself does not support color interpolation in this way. The best you can do is a GradientPaint, but this is a poor, slow, memory expensive approximation when you want to color splines as I did.
Although I haven't exhaustively looked through the iText API, I couldn't see anything that could be used to interpolate the color in the way I needed. No-one on the iText mailing list knew how to do it.
The PDF standard does support exactly what I want via Axial Shading (ISO 32000-1:2008, 8.7.4.5.3). So the capability is there, is just doesn't seem to be exposed in iText.

In the end, I unfortunately had to ditch rendering to PDF and go back to a high-res offscreen PGraphicsJava2D. I can render to this @ 300dpi for a 20x30 inch canvas no problems (I'll be making large prints).

Hope this helps someone in the future.

lasko25

Re: Changing vertex() color within beginShape()

10 months ago

Sorry if I am just missing something here, but did you end up getting high-res rendering with color interpolation within begin/endShape()?

I would gladly just use OPENGL but I am also rendering images, and it just renders so slow unless I am using the default P2D renderer.

Thanks.

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