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Forum Update on Monday, May 27th 2025

Matrix operations

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qmatrixqmatrix4x4qgenericmatrix
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  • ? A Former User

    Okay, sorry, seems like I don't understand what kind of maths you intent to do with it. I thought you needed some basic transforms, like rotation, scale, and such.

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    doubitchou
    wrote on last edited by
    #9

    @Wieland
    That's right : basic tranform, rotation, scale are fine. But size 3x3 is not enough: the one I have like the link I provide in my example is a 8x8

    ? 1 Reply Last reply
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    • D doubitchou

      @Wieland
      That's right : basic tranform, rotation, scale are fine. But size 3x3 is not enough: the one I have like the link I provide in my example is a 8x8

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      ? Offline
      A Former User
      wrote on last edited by A Former User
      #10

      @doubitchou Just out of curiosity, can you provide some equations? Because I really don't get what you mean when you have a 2D problem and you say you want to rotate a 8x8 matrix.

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      • ? A Former User

        @doubitchou Just out of curiosity, can you provide some equations? Because I really don't get what you mean when you have a 2D problem and you say you want to rotate a 8x8 matrix.

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        doubitchou
        wrote on last edited by
        #11

        @Wieland

        As a use case let's consider you have the 8x8 leds backpack which can have 3 values (representing colors in that case)

        0 : off
        1 : Green
        2 : Red
        3 : Orange (Green + Red btw)

        Therefore, if I want to draw my 1st line as Red and the Second as Green :

        22222222
        11111111
        00000000
        00000000
        00000000
        00000000
        00000000
        00000000

        And when I want to rotate right it would be :

        00000012
        00000012
        00000012
        00000012
        00000012
        00000012
        00000012
        00000012

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        • ? Offline
          ? Offline
          A Former User
          wrote on last edited by A Former User
          #12

          Oh, now I get it. This has nothing to do with the usual rotate, translate, scale,... transforms. There are no functions for this readily available in our framework. You need to implement that all by yourself.

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          • ? A Former User

            Oh, now I get it. This has nothing to do with the usual rotate, translate, scale,... transforms. There are no functions for this readily available in our framework. You need to implement that all by yourself.

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            doubitchou
            wrote on last edited by
            #13

            @Wieland said in Matrix operations:

            Oh, now I get it. This has nothing to do with the usual rotate, translate, scale,... transforms. There are no functions for this readily available in our framework. You need to implement that all by yourself.

            Indeed this is what I was just thinking ... since the VRonin answer.

            Thanks to both of you

            kshegunovK 1 Reply Last reply
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            • D doubitchou

              @Wieland said in Matrix operations:

              Oh, now I get it. This has nothing to do with the usual rotate, translate, scale,... transforms. There are no functions for this readily available in our framework. You need to implement that all by yourself.

              Indeed this is what I was just thinking ... since the VRonin answer.

              Thanks to both of you

              kshegunovK Offline
              kshegunovK Offline
              kshegunov
              Moderators
              wrote on last edited by
              #14

              What you described is called a matrix transposition. My advice - Just use Eigen, it's headers-only anyway.

              Read and abide by the Qt Code of Conduct

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              • kshegunovK kshegunov

                What you described is called a matrix transposition. My advice - Just use Eigen, it's headers-only anyway.

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                doubitchou
                wrote on last edited by
                #15

                @kshegunov said in Matrix operations:

                What you described is called a matrix transposition. My advice - Just use Eigen, it's headers-only anyway.

                Oh ? Great I was about implementing all by myself.
                Thanks for this

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                • D doubitchou

                  @VRonin

                  Thanks for your answer.
                  Now I understand that this is not a "standard" container as I thought, indeed .

                  By "Basic Matrix Capabilities" I meant a little more than storing like vector or array do, it was more a comparison to big math. libraries like Eigen or Blaze.
                  Actually I'd need some minimal matrix functions like rotation, inverse, flip

                  VRoninV Offline
                  VRoninV Offline
                  VRonin
                  wrote on last edited by VRonin
                  #16

                  @doubitchou said in Matrix operations:

                  Actually I'd need some minimal matrix functions like rotation, inverse, flip

                  if by rotation and inverse you don't mean the mathematical terms linked but physical movements of the image in the leds, all these operations can be easily done just by acting on the indexes rather than the content of the matrix.

                  For example:
                  given a matrix[rowCount][colCount]

                  matrix[i][j]

                  • mirrored on the vertical axis is matrix[i][colCount-j-1]
                  • rotated 90° counter-clockwise is matrix[j][i]

                  "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                  ~Napoleon Bonaparte

                  On a crusade to banish setIndexWidget() from the holy land of Qt

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                  • VRoninV VRonin

                    @doubitchou said in Matrix operations:

                    Actually I'd need some minimal matrix functions like rotation, inverse, flip

                    if by rotation and inverse you don't mean the mathematical terms linked but physical movements of the image in the leds, all these operations can be easily done just by acting on the indexes rather than the content of the matrix.

                    For example:
                    given a matrix[rowCount][colCount]

                    matrix[i][j]

                    • mirrored on the vertical axis is matrix[i][colCount-j-1]
                    • rotated 90° counter-clockwise is matrix[j][i]
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                    doubitchou
                    wrote on last edited by
                    #17

                    To provide a better understanding I've put some design concepts :

                    concepts

                    As you can see these are basic operations

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                    • VRoninV Offline
                      VRoninV Offline
                      VRonin
                      wrote on last edited by VRonin
                      #18

                      You could even use QImage with QImage::Format_Mono format as a container actually

                      "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                      ~Napoleon Bonaparte

                      On a crusade to banish setIndexWidget() from the holy land of Qt

                      D 1 Reply Last reply
                      0
                      • VRoninV VRonin

                        You could even use QImage with QImage::Format_Mono format as a container actually

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                        doubitchou
                        wrote on last edited by
                        #19

                        @VRonin said in Matrix operations:

                        You could even use QImage with QImage::Format_Mono format as a container actually

                        I'm not sure to understand it right

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                        0
                        • VRoninV Offline
                          VRoninV Offline
                          VRonin
                          wrote on last edited by
                          #20

                          QImage myMatrix(8,8,QImage::Format_Mono) will create a container of 8 by 8 bits (not bytes).

                          • myMatrix.fill(0); to turn everything off.
                          • Point: myMatrix.setPixel(0,0,1);
                          • Line(1): for(int i=0;i<myMatrix.width();++i) myMatrix.setPixel(0,i,1);
                          • Column(1): for(int i=0;i<myMatrix.height();++i) myMatrix.setPixel(i,0,1);
                          • Border: for(int i=0;i<myMatrix.width();++i) {myMatrix.setPixel(0,i,1); myMatrix.setPixel(myMatrix.height()-1,i,1);} for(int i=0;i<myMatrix.height();++i) {myMatrix.setPixel(i,0,1); myMatrix.setPixel(i,myMatrix.width()-1,1);}
                          • Column Shift(1): myMatrix=myMatrix.transformed(QTransform().translate(1,0));
                          • Column Shift(-1): myMatrix=myMatrix.transformed(QTransform().translate(-1,0));
                          • Line Shift(1): myMatrix=myMatrix.transformed(QTransform().translate(0,1));
                          • Line Shift(-1): myMatrix=myMatrix.transformed(QTransform().translate(0,-1));
                          • Rotate(1): myMatrix=myMatrix.transformed(QTransform().rotate(270));
                          • Rotate(-1): myMatrix=myMatrix.transformed(QTransform().rotate(90));
                          • Invert: myMatrix.invertPixels();

                          "La mort n'est rien, mais vivre vaincu et sans gloire, c'est mourir tous les jours"
                          ~Napoleon Bonaparte

                          On a crusade to banish setIndexWidget() from the holy land of Qt

                          D 1 Reply Last reply
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                          • VRoninV VRonin

                            QImage myMatrix(8,8,QImage::Format_Mono) will create a container of 8 by 8 bits (not bytes).

                            • myMatrix.fill(0); to turn everything off.
                            • Point: myMatrix.setPixel(0,0,1);
                            • Line(1): for(int i=0;i<myMatrix.width();++i) myMatrix.setPixel(0,i,1);
                            • Column(1): for(int i=0;i<myMatrix.height();++i) myMatrix.setPixel(i,0,1);
                            • Border: for(int i=0;i<myMatrix.width();++i) {myMatrix.setPixel(0,i,1); myMatrix.setPixel(myMatrix.height()-1,i,1);} for(int i=0;i<myMatrix.height();++i) {myMatrix.setPixel(i,0,1); myMatrix.setPixel(i,myMatrix.width()-1,1);}
                            • Column Shift(1): myMatrix=myMatrix.transformed(QTransform().translate(1,0));
                            • Column Shift(-1): myMatrix=myMatrix.transformed(QTransform().translate(-1,0));
                            • Line Shift(1): myMatrix=myMatrix.transformed(QTransform().translate(0,1));
                            • Line Shift(-1): myMatrix=myMatrix.transformed(QTransform().translate(0,-1));
                            • Rotate(1): myMatrix=myMatrix.transformed(QTransform().rotate(270));
                            • Rotate(-1): myMatrix=myMatrix.transformed(QTransform().rotate(90));
                            • Invert: myMatrix.invertPixels();
                            D Offline
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                            doubitchou
                            wrote on last edited by doubitchou
                            #21

                            @VRonin

                            Great answer !, especially to be adapted to my needs. Anyway, I think I should try with Format_Indexed8 instead as I need to store the color values which requires more than a single bit:

                            0 : off
                            1 : Green
                            2 : Red
                            3 : Orange

                            (Merci pour cette réponse)

                            1 Reply Last reply
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