Using different QR version

[peterkorolev]

Hi!

Is it possible to use a lower version of QR code? With lower resolution/memory

[anunpanya]

@peterkorolev It's possible, but must find a pattern version of QR Code is smaller than this.

[marsrakete]

He probably means "lower ECC". I have the same issue, the generated QR has a lot of redundancy and uses very small pixes (one pixel QR = 1 pixel OLED). I'd need lower ECC version which might generate QRs with 1 Pixel QR = 4 Pixel OLED: The original Arduino qrence library does offer generation between ECC 1 and 4. I need to look that up.

[ben-mkiv]

this lib works pretty fine for me:
https://github.com/nayuki/QR-Code-generator/tree/master/c

allows to autopick the lowest possible version and auto adjusts ECC

put the qrcodegen.c / qrcodegen.h files from the project above in the same directory as the following 2 files and it should work (only tested on esp32 with esp-idf and arduino-esp32 lib)

qrencode.h

#include "OLEDDisplay.h"
#include "qrcodegen.h"

// https://www.qrcode.com/en/about/version.html QR version overview
#define QRENCODE_VERSION_MIN (1)
#define QRENCODE_VERSION_MAX (7) // should work up to 11 (61 x 61)

class QREncode
{
private:
    String QRBuffer = "";
    uint8_t code[qrcodegen_BUFFER_LEN_FOR_VERSION(QRENCODE_VERSION_MAX)];
    int resolution = 0;
    char maxScale = 0;

    void create(OLEDDisplay *display, String message);
    void render(OLEDDisplay *display, int x, int y);

public:
    void render(OLEDDisplay *display, String message, int x, int y){
        create(display, message);
        render(display, x, y);
    }
};

qrencode.cpp

#include "qrencode.h"

void QREncode::create(OLEDDisplay *display, String message) {
    // dont reencode code if nothing changed
    if(message.equals(QRBuffer))
        return;

    QRBuffer = message;
    uint8_t buffer[qrcodegen_BUFFER_LEN_FOR_VERSION(QRENCODE_VERSION_MAX)];

    resolution = 0;
    maxScale = 1;

    if(qrcodegen_encodeText(message.c_str(), &buffer[0], &code[0], qrcodegen_Ecc_LOW, QRENCODE_VERSION_MIN, QRENCODE_VERSION_MAX, qrcodegen_Mask_AUTO, true)){
        resolution = qrcodegen_getSize(code);

        while((maxScale + 1) * resolution < display->height())
            maxScale++;

        printf("QR created, size: %d, scale factor: %d", resolution, maxScale);
    }
    else {
        printf((char *) "failed to create QR code");
    }
}

void QREncode::render(OLEDDisplay *display, int x, int y) {
    int renderResolution = resolution * maxScale;
    int offsetX = x + (display->height() - renderResolution) / 2;
    int offsetY = y + (display->height() - renderResolution) / 2;

    display->fillRect(offsetX - 2, offsetY - 2, renderResolution + 4, renderResolution + 4);

    // draw QR Code
    for (char x = 0; x < renderResolution; x++) {
        for (char y = 0; y < renderResolution; y++) {
            display->setPixelColor(offsetX + x, offsetY + y, qrcodegen_getModule(code, x / maxScale, y / maxScale) ? BLACK : WHITE);
        }
    }
}

[nayuki]

@ben-mkiv Pretty good answer, but a few corrections:

• Do not #include C code into a C++ source file! These are different languages which are not 100% compatible. The proper way is to #include the .h file into the .cpp file, then compile the .c and .cpp files separately. If you are using the Arduino IDE, separate compilation will work out of the box.
• You cannot #define QRENCODE_VERSION_MIN (0), because the minimum version must be at least 1. You'll trigger an assertion error at the top of qrcodegen_encodeSegmentsAdvanced(); otherwise you might smash an array.

[ben-mkiv]

Thanks @nayuki, i've edited my post according to your suggestions.

I've included the c file because it didn't compile for me with just the header (using CLion with ESP-IDF, so i probably just have to make it it's own component or fiddle with the CMake config)