loadImage(...) and createGraphics(..., P2D) have different y-coordinates

Most appropriate sub-area of Processing 4?

OpenGL

Processing version

4.4.4

Operating system

MacOSX

Steps to reproduce this

PShader texCoordShader;
PGraphics pgP2D, pgDefault;

void setup() {
  size(800, 400, P2D);
  
  String fragShader = 
    "#ifdef GL_ES\n" +
    "precision mediump float;\n" +
    "#endif\n" +
    "varying vec4 vertTexCoord;\n" +
    "void main() {\n" +
    "  gl_FragColor = vec4(vertTexCoord.st, 0.0, 1.0);\n" +
    "}";


  saveStrings("frag.glsl", split(fragShader, "\n"));
  texCoordShader = loadShader("frag.glsl");//, "vert.glsl");

  pgP2D = createGraphics(400, 400, P2D);
  pgDefault = createGraphics(400, 400); // Default JAVA2D renderer

  pgP2D.beginDraw();
  pgP2D.endDraw();

  pgDefault.beginDraw();
  pgDefault.endDraw();
}

void draw() {
  background(0);
  shader(texCoordShader);
  image(pgP2D, 0, 0);
  image(pgDefault, 400, 0);
}

Additional context

I'm working on a keystone library that is using a shader.
Because a image has different coordinates then a graphics created with P2D I need to know what the user is giving.
Not only that, it complicates the shader math way more then I would like.

To give an example:

The difference between those is P2D and default renderer (both in a sketch that is P2D).
Notice that the text is correct in both cases!!!

This does not just apply for PGraphics, using loadImage is different as well (cause also baked by a BufferedImage).
Having a mix of both of them really complicate things.
Complaining is easy however. I will dig into seeing if I can find a solution.

Would you like to work on the issue?

Trying...

Riproduci lo sketch fornito e confronta il comportamento delle coordinate della texture di loadImage(...) con quello di createGraphics(..., P2D), incluso il percorso BufferedImage e l’output dello shader. Parti da questi punti di ingresso e da PGraphics, quindi determina se la convenzione delle coordinate può essere resa coerente; il lavoro è completato quando entrambe le sorgenti di immagini producono lo stesso orientamento y sotto lo shader.