coordinates by reverse use of matrix to get original value

[meDerekD17]

After scaling and translating, i tap on the screen. I use the values from MatrixDecompose (translation , scale) to go back to the 'real world without translation and scale' coordinates. They value are always off in Y by the same amount. I am fairly sure it is caused by the AppBar distance. When I remove the AppBar values work.
My problem is I I am not completely sure what is happening, so I might get it wrong on different devices. Also, I would prefer to be able to use the Appbar. I can not find a solution of finding AppBar height. Any Suggestions? What have others done with this problem?

[meDerekD17]

But I notice if I do not enlarge the object on the screen (scale = 1.0) there is no problem. This makes me think I do not understand everything. I use
decomposeToValues(matrix) to get translation and scale.
I use details.globalPosition to get an Offset (localOffset)
then to get the real world coordinates I use:
Offset baseOffset = (localOffset - matrixValue.translation) / matrixValue.scale;

[Venusdjinni]

Hello, please did you manage to find a solution for this? I am facing the exact same issue

[meDerekD17]

I will see if I can fine my GitHub account information to sign on to GitHub and go over what was said before. I did get it to work for what I wanted, and it has worked OK

…

On Dec 18, 2022, at 7:07 PM, Venusdjinni ***@***.***> wrote: Hello, please did you manage to find a solution for this? I am facing the exact same issue — Reply to this email directly, view it on GitHub <#16 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABW7LCK3J2GZM52NLFVSMUDWN6KLRANCNFSM4MNWL57A>. You are receiving this because you authored the thread.

[meDerekD17]

I think the comments above are what I did. I do not do any rotation, but I do allow translation and scale, and it works. I think what I was concerned about is that I did not quite understand everything, and so something might not work with a different device. But it has worked OK. Maybe if you can say what you have written and what problems you have?

[Venusdjinni]

I am building an image editor, and what I want is to convert the transformation of a widget into 'real scale' values. I managed to do it accurately when there is no scale or rotation, but whenever I enable one of them, MatrixGestureDetector.decompose gives me a bad translation offset

[meDerekD17]

I did not do rotation, but I did get scale and offset (Translate/move of origin) to work. Sometimes knowing that something works does allow solving. It is getting a bit late here.

[meDerekD17]

In my gesture detector I have:

//GestureDetector activates 3 'handle' methods below to account for screen
//scale and translation (not rotation)
void _handleScaleStart(ScaleStartDetails details) {
//print('scaleStart details: ${details}');
//from MatrixGestureDetector - onScaleStart()to
//seems to be when user does initial touch to drag the screen
//focal point is where screen touched. Initializes drag/scale for Board screen
// widget.scaleTranslateMatrices.translationUpdater.value = details.focalPoint;
// widget.scaleTranslateMatrices.scaleUpdater.value = 1.0;
//now using singleton class
scaleTranslateMatrices.translationUpdater.value = details.focalPoint;
scaleTranslateMatrices.scaleUpdater.value = 1.0;
setState(() {});
}

void _handleScaleUpdate(ScaleUpdateDetails details) {
//uses singleton class
if(referencedData.bOneOfBeginnerHelpsAreShowing) return;
scaleTranslateMatrices.translationDeltaMatrix = Matrix4.identity();
scaleTranslateMatrices.scaleDeltaMatrix = Matrix4.identity();

Offset translationDelta = scaleTranslateMatrices.translationUpdater
    .update(details.focalPoint);

//attempt draw 'real' top Left - works for translates & practical zooms
referencedData.osUntransformedTopLeft -=
    translationDelta; //works for translate

scaleTranslateMatrices.translationDeltaMatrix =
    scaleTranslateMatrices.translate(translationDelta);
scaleTranslateMatrices.matrix =
    scaleTranslateMatrices.translationDeltaMatrix *
        scaleTranslateMatrices.matrix; //problem

Offset focalPoint;
RenderBox renderBox = context.findRenderObject();
focalPoint = renderBox.globalToLocal(details.focalPoint);

if (details.scale != 1.0) {
  double scaleDelta =
  scaleTranslateMatrices.scaleUpdater.update(details.scale);

  scaleTranslateMatrices.scaleDeltaMatrix =
      scaleTranslateMatrices.scale(scaleDelta, focalPoint);
  scaleTranslateMatrices.matrix =
      scaleTranslateMatrices.scaleDeltaMatrix *
          scaleTranslateMatrices.matrix;
}
scaleTranslateMatrices.notifier.value =
    scaleTranslateMatrices.matrix;
setState(() {});

}

void _handleScaleReset() {
//double tap causes Game screen to reset to default scale and position
scaleTranslateMatrices
.resetMatrices(); //reset Matrix4s back to initial values
referencedData.osUntransformedTopLeft = Offset(0.0, 0.0);
setState(() {});
}

@OverRide
Widget build(BuildContext context) {
return GestureDetector(
.......
I think any functions called are in the original library. I could have another look tomorrow if you have further questions

[Venusdjinni]

Thank you. I will have a look at it tomorrow, it's pretty late here too

[Venusdjinni]

Okay I see that you managed the scale using the focal point. Can you share the implementation of scaleTranslateMatrices's class?

[meDerekD17]

I am not at my computer now, but that class is probably in the original code of the package. I will have a look in a few minutes

…

Sent from my iPhone

On Dec 19, 2022, at 7:56 AM, Venusdjinni ***@***.***> wrote: Okay I see that you managed the scale using the focal point. Can you share the implementation of scaleTranslateMatrices's class? — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you authored the thread.

[meDerekD17]

I have to go to do something with snow. But I have a file named: matrices_classes.dart. It may be that the original has changed since a couple of years ago. I can see a lot of the functions match, but not all:
//Classes used in matrix manipulation for scale and translation(offsets)
//uses features and code of MatrixGestureDetector - But no rotation
//from
//https://github.com/pskink/matrix_gesture_detector/blob/master/lib/matrix_gesture_detector.dart

import 'package:flutter/material.dart';

//based on Matrix Gesture Detector
// From: https://github.com/pskink/matrix_gesture_detector

class MatrixDecomposedValues {
/// Translation, in most cases useful only for matrices that are nothing but
/// a translation (no scale and no rotation).
final Offset translation;

/// Scaling factor.
final double scale;

//2022Aug1 - removed rotation, was not used anyway
/// Rotation in radians, (-pi..pi) range.
//final double rotation; //But we don't include rotation

MatrixDecomposedValues(this.translation, this.scale);
//, this.rotation);

@OverRide
String toString() {
return 'MatrixDecomposedValues(translation: $translation, ' +
'scale: ${scale.toStringAsFixed(3)}';
// ', rotation: ${rotation.toStringAsFixed(3)})';
}
} //class MatrixDecomposedValues {

//From MatrixGestureDetector
//appears to set up a class to hold a value, and return (probably) difference
//between old value and new value.
//Difference needed as applying to Matrices, and want changes - maybe??
typedef _OnUpdate = T Function(T oldValue, T newValue);

class _ValueUpdater {
final _OnUpdate onUpdate;
T value;

_ValueUpdater({this.onUpdate});

T update(T newValue) {
T updated = onUpdate(value, newValue);
value = newValue;
return updated;
}
}

class ScaleTranslateMatrices {
//appears to be a Singleton class, with, sort of, passed parameters
//that are initialized in constructor
ScaleTranslateMatrices._privateConstructor(){
//
translationDeltaMatrix = Matrix4.identity();
scaleDeltaMatrix = Matrix4.identity();
matrix = Matrix4.identity();
notifier = ValueNotifier(matrix);
}

static final ScaleTranslateMatrices instance = ScaleTranslateMatrices
._privateConstructor();

Matrix4 matrix;
ValueNotifier notifier;
Matrix4 translationDeltaMatrix;
Matrix4 scaleDeltaMatrix;

void resetMatrices() {
//go back to default view
translationDeltaMatrix = Matrix4.identity();
scaleDeltaMatrix = Matrix4.identity();
matrix = Matrix4.identity();
notifier = ValueNotifier(matrix); //is needed
}

// Decomposes [matrix] into [MatrixDecomposedValues.translation],
// [MatrixDecomposedValues.scale] and [MatrixDecomposedValues.rotation]
// components.
static MatrixDecomposedValues decomposeToValues(Matrix4 matrix) {
var array = matrix.applyToVector3Array([0, 0, 0, 1, 0, 0]);
Offset translation = Offset(array[0], array[1]);
Offset delta = Offset(array[3] - array[0], array[4] - array[1]);
double scale = delta.distance;
double rotation = delta.direction;
return MatrixDecomposedValues(translation, scale);
//, rotation);
}

//Matrix creation from GestureDetector - composed from translation and scale
// Compose the matrix from translation, scale.
// pass a null to skip any matrix from composition.
// If [matrix] is not null the result of the composing will be concatenated
// to that [matrix], otherwise the identity matrix will be used.
static Matrix4 compose(
Matrix4 matrix, Matrix4 translationMatrix, Matrix4 scaleMatrix) {
if (matrix == null) matrix = Matrix4.identity();
if (translationMatrix != null) matrix = translationMatrix * matrix;
if (scaleMatrix != null) matrix = scaleMatrix * matrix;
return matrix;
}

//hold values and differences in values
_ValueUpdater translationUpdater = _ValueUpdater(
onUpdate: (oldVal, newVal) => newVal - oldVal,
);

_ValueUpdater scaleUpdater = _ValueUpdater(
onUpdate: (oldVal, newVal) => newVal / oldVal,
);

Matrix4 translate(Offset translation) { //was _translate
//create the translation matrix from dx,dy translation
var dx = translation.dx;
var dy = translation.dy;
// ..[0] = 1 # x scale
// ..[5] = 1 # y scale
// ..[10] = 1 # diagonal "one"
// ..[12] = dx # x translation
// ..[13] = dy # y translation
// ..[15] = 1 # diagonal "one"
return Matrix4(1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, dx, dy, 0, 1);
}

Matrix4 scale(double scale, Offset focalPoint) { //was_scale
//create scale matrix from scale, and focal point (to be clarified***)
var dx = (1 - scale) * focalPoint.dx;
var dy = (1 - scale) * focalPoint.dy;
// ..[0] = scale # x scale
// ..[5] = scale # y scale
// ..[10] = 1 # diagonal "one"
// ..[12] = dx # x translation
// ..[13] = dy # y translation
// ..[15] = 1 # diagonal "one"
return Matrix4(scale, 0, 0, 0, 0, scale, 0, 0, 0, 0, 1, 0, dx, dy, 0, 1);
}
} //Singleton class ScaleTranslateMatrices