32x16 LED panel : troubles to drawPixel at 0,0

[PhilBauch]

I tried your nice library with 64x32 panel P4 (always using single panel in my dev), but needed to improve visibility/brightness, thus decided to test a 128x64 P2 (not very successful in this attempt...) and a 32x16 P8 (always trying to keep the same occupied surface)
This 32x16 P8 panel look promising for better visibility/brightness, but it raises issues.

So I tried to test very basic scenarii, including drawing pixels one by one, relying on your discussion #622
The full panel has been filled, but in an awkward manner, thus I decided to simplify your loop example to draw only ONE single pixel at (0, 0), and here is the result:

I asked the FactSheet of the panel to the reseller, but all I got was an answer about "IC parameters are:"

I got not so much information from the product on AliExpress (except it is a 1/4 scan):
https://www.aliexpress.com/item/1005005692881899.html?spm=a2g0o.order_list.order_list_main.5.281a1802hNz9vE#nav-specification

The only other information I have about the panel is its markup:

The project I am working on is a device to install on the rear window of a car to detect dangerous situations and to warn the following driver that comes too close.
So it is important to minimize space occupancy to keep good rear visibility to the "protected" driver with the central mirror.
But on the other hand it is also important to be as bright as possible to inform the following driver about the risk of coming too close.
Thus I need to be able to use appropriate fonts and colors (plus potentially some icons) depending on the criticality of the situation.
This is not a device to send fines to the following driver, it has pedagogical purpose, as it provides only facts, i.e. the distance in meters, plus in (tenths of) seconds - considering the speed - before a crash, as well as an estimate of the level of danger (color code)

[PhilBauch]

The modified code is the following:
`
/*************************************************************************
Description:

The underlying implementation of the ESP32-HUB75-MatrixPanel-I2S-DMA only
supports output to HALF scan panels - which means outputting
two lines at the same time, 16 or 32 rows apart if a 32px or 64px high panel
respectively.
This cannot be changed at the DMA layer as it would require a messy and complex
rebuild of the library's internals.

However, it is possible to connect QUARTER (i.e. FOUR lines updated in parallel)
scan panels to this same library and
'trick' the output to work correctly on these panels by way of adjusting the
pixel co-ordinates that are 'sent' to the ESP32-HUB75-MatrixPanel-I2S-DMA
library.

**************************************************************************/

/* Use a custom Virtual Display class to re-map co-ordinates such that they draw
correctly on a 32x16 1/4 Scan panel (or chain of such panels).
*/
#include "ESP32-VirtualMatrixPanel-I2S-DMA.h"

/* ================================================== */
// Define custom class derived from VirtualMatrixPanel
class EightPxBasePanel : public VirtualMatrixPanel
{
public:
using VirtualMatrixPanel::VirtualMatrixPanel; // inherit VirtualMatrixPanel's constructor(s)

protected:

VirtualCoords getCoords(int16_t x, int16_t y);  // custom getCoords() method for specific pixel mapping

};

// define custom getCoords() method for specific pixel mapping
inline VirtualCoords EightPxBasePanel ::getCoords(int16_t x, int16_t y) {

coords = VirtualMatrixPanel::getCoords(x, y); // first call base class method to update coords for chaining approach

if ( coords.x == -1 || coords.y == -1 ) { // Co-ordinates go from 0 to X-1 remember! width() and height() are out of range!
return coords;
}

uint8_t pxbase = 8; // pixel base
if ((coords.y & 4) == 0)
{
coords.x = (coords.x / pxbase) * 2 * pxbase + pxbase + 7 - (coords.x & 0x7); // 1st, 3rd 'block' of 8 rows of pixels, offset by panel width in DMA buffer
}
else
{
coords.x += (coords.x / pxbase) * pxbase; // 2nd, 4th 'block' of 8 rows of pixels, offset by panel width in DMA buffer
}

coords.y = (coords.y >> 3) * 4 + (coords.y & 0b00000011);

return coords;
}
/* ================================================== */
// Panel configuration
#define PANEL_RES_X 32 // Number of pixels wide of each INDIVIDUAL panel module.
#define PANEL_RES_Y 16 // Number of pixels tall of each INDIVIDUAL panel module.

#define NUM_ROWS 1 // Number of rows of chained INDIVIDUAL PANELS
#define NUM_COLS 1 // Number of INDIVIDUAL PANELS per ROW

// ^^^ NOTE: DEFAULT EXAMPLE SETUP IS FOR A CHAIN OF TWO x 1/8 SCAN PANELS

// Change this to your needs, for details on VirtualPanel pls read the PDF!
#define SERPENT true
#define TOPDOWN false
#define VIRTUAL_MATRIX_CHAIN_TYPE CHAIN_TOP_RIGHT_DOWN

// placeholder for the matrix object
MatrixPanel_I2S_DMA *dma_display = nullptr;

// placeholder for the virtual display object
EightPxBasePanel *FourScanPanel = nullptr;

// PHB (2025/06/11) : Define specific pinout
#define PIN_CLK 32 // instead of default to 16
#define PIN_D 33 // instead of default to 17
#define PIN_E -1 // PHB (2025/06/11) : do not use pin 18

/******************************************************************************
Setup!
******************************************************************************/
void setup()
{
delay(250);

Serial.begin(115200);
Serial.println(""); Serial.println(""); Serial.println("");
Serial.println("");
Serial.println("* 1/8 Scan Panel Demonstration *");
Serial.println("");

/*
// 62x32 1/8 Scan Panels don't have a D and E pin!

   PHB (2025/06/11) : Those are not defined to get relevant pins...

   HUB75_I2S_CFG::i2s_pins _pins = {
    R1_PIN, G1_PIN, B1_PIN, R2_PIN, G2_PIN, B2_PIN,
    A_PIN, B_PIN, C_PIN, D_PIN, E_PIN,
    LAT_PIN, OE_PIN, CLK_PIN
   };

*/

HUB75_I2S_CFG mxconfig(
PANEL_RES_X * 2, // DO NOT CHANGE THIS
PANEL_RES_Y / 2, // DO NOT CHANGE THIS
NUM_ROWS * NUM_COLS // DO NOT CHANGE THIS
//,_pins // Uncomment to enable custom pins : Done by PHB (2025/06/11)
);

// PHB (2025/06/11) : Set specific pins
mxconfig.gpio.d = PIN_D;
mxconfig.gpio.clk = PIN_CLK;

mxconfig.clkphase = false; // Change this if you see pixels showing up shifted wrongly by one column the left or right.

//mxconfig.driver = HUB75_I2S_CFG::FM6126A; // in case that we use panels based on FM6126A chip, we can set it here before creating MatrixPanel_I2S_DMA object

// OK, now we can create our matrix object
dma_display = new MatrixPanel_I2S_DMA(mxconfig);

// let's adjust default brightness to about 75%
// dma_display->setBrightness8(40); // range is 0-255, 0 - 0%, 255 - 100%
dma_display->setBrightness8(255); // range is 0-255, 0 - 0%, 255 - 100%

// Allocate memory and start DMA display
if ( not dma_display->begin() )
Serial.println("****** !KABOOM! I2S memory allocation failed ***********");

dma_display->clearScreen();
delay(500);

// create FourScanPanellay object based on our newly created dma_display object
FourScanPanel = new EightPxBasePanel ((*dma_display), NUM_ROWS, NUM_COLS, PANEL_RES_X, PANEL_RES_Y, VIRTUAL_MATRIX_CHAIN_TYPE);

// THE IMPORTANT BIT BELOW!
// FOUR_SCAN_16PX_HIGH
// FOUR_SCAN_32PX_HIGH
// **** You don't need to set PhysicalPanelScanRate when use your own virtual panel class
//FourScanPanel->setPhysicalPanelScanRate(FOUR_SCAN_16PX_HIGH);
}

// Test the pixel mapping - fill the panel pixel by pixel
void loop() {

int i = 0;
int j = 0;
//for (int i = 0; i < FourScanPanel->height(); i++)
{
//for (int j = 0; j < FourScanPanel->width(); j++)
{
Serial.printf("j = %i , i = %i , GPIO.CLK = %i , GPIO.D = %i , GPIO.E = %i \n", j, i
, dma_display->getCfg().gpio.clk, dma_display->getCfg().gpio.d, dma_display->getCfg().gpio.e);

  FourScanPanel->drawPixel(j, i, FourScanPanel->color565(255, 255, 0));
  delay(30);
}

}

delay(2000);
dma_display->clearScreen();

} // end loop
`

[PhilBauch]

I do not understand why code snippet does not appear as expected when I preview it ...
Not so fluent in github usage...

[board707]

Hi

It is too early to try a code with Virtual coords function using a pixbase like this:

uint8_t pxbase = 8; // pixel base
if ((coords.y & 4) == 0)
{
coords.x = (coords.x / pxbase) * 2 * pxbase + pxbase + 7 - (coords.x & 0x7); 

... etc...

First you need to figure out the line switching mode of the panel.

Judging by the fact that there is no separate line switch chips on the panel, but instead there are just DP4953 MOSFETs - this is the so-called direct switching. This is a common option for 2 or 4 scan panels.
Unfortunately, as far as I know, this type of switching is not supported in this library yet.

[PhilBauch]

Thanks for your return, even if what determines the "line switching" is still a little unclear to me...
From what I understood, the library does not support the type of switching I have on my LED panel, and it is not likely to be proposed so soon ?
Thus all 1/2 and 1/4 scan panels have to be prohibited for my project (where I wish to control display from an ESP32 thru HUB75) ?
Do you have some recommendations of suitable LED panels to fit with these requirements:
1- 256x128 mm dimension
2- the brightest and most visible at daylight from 3 to 15 meters (don't know whether 128x64 or 64x32 or 32x16, i.e. P2 or P4 or P8, is the best for that)
3- compatible with your nice library...

I should say that it is very cumbersome to fetch an exact FactSheet with all relevant information plus guidance on the LED panels related products proposed on AliExpress
The vendor of my P8 panel tells that I need a specific control card (Huidu HD -WF1 or Huidi-D16), by that does not match my need, plus prices go from 3,63$ to 47,95$ (gasp!), but it imposes a specific app (HD2020 and LedArt)

[mrcodetastic]

Unfortunately, as far as I know, this type of switching is not supported in this library yet.

Hi @board707 - Does your library support these boards? I'd be interested to look at the code if so.

[mrcodetastic]

Thanks for your return, even if what determines the "line switching" is still a little unclear to me... From what I understood, the library does not support the type of switching I have on my LED panel, and it is not likely to be proposed so soon ? Thus all 1/2 and 1/4 scan panels have to be prohibited for my project (where I wish to control display from an ESP32 thru HUB75) ?

Can you try seeing if there's any combination that works with the PxMatrix library?

[board707]

I'd be interested to look at the code if so.

Hi @mrcodetastic
The code is rather simple.
Let's take a 4S matrix as an example.
In this case, each of the four lines is controlled by its own pin from ABCD set, so you give HIGH to the pin you want to turn on and LOW to all the others.
Sometimes you come across panels that are controlled by a LOW level, otherwise the principle is the same.

[mrcodetastic]

I'd be interested to look at the code if so.

Hi @mrcodetastic
The code is rather simple.
Let's take a 4S matrix as an example.
In this case, each of the four lines is controlled by its own pin from ABCD set, so you give HIGH to the pin you want to turn on and LOW to all the others.
Sometimes you come across panels that are controlled by a LOW level, otherwise the principle is the same.

Right. So I just need to modify the library to invert the address lines?

[board707]

I may be wrong, but you don't have such a method of switching lines yet.
So answer No.

[mrcodetastic]

@PhilBauch - Let me look into this one for you. Should be relatively easy to implement.

[PhilBauch]

@mrcodetastic - Thank you in advance for at least trying to implement the solution.
This difficulty in controlling drawing a single pixel was not a good sign for me, as the final goal for my project is to display characters using relevant fonts for the panel size.
I will read your feedback with great interest.