processing/processing

Shape with only two vertices won't draw (P2D and P3D, works with JAVA2D)

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#5,270 opened on Sep 23, 2017

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help wantedlowopengl

Description

Description

A shape with only two vertices in immediate mode won't render; it appears when adding a third vertex. This issue presents itself only with the hardware renderers.

Steps to Reproduce

void setup(){
  size(200, 200, P2D);
  noFill();
  stroke(0);
  beginShape();
  vertex(10, 10);
  vertex(100, 100);
  endShape();
}

Your Environment

Processing version: 3.3.6 Operating System and OS version: macOS 10.12.6

Contributor guide

Tech stack
java
Domain
frontend
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
JavaProcessing API
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the rendering code for beginShape() and vertex() in the P2D and P3D renderers (likely in PGraphicsOpenGL.java). The issue is that shapes with only two vertices do not draw, but adding a third vertex renders correctly. Look at how the shape vertex list is processed and whether there is a minimum vertex count check that incorrectly omits lines. The fix may involve handling the case of a single line segment (two vertices) in the OpenGL path.