I ran the scrolling example, but the screen seemed to have a residual image and refresh slowly

[ShiPC123]

I used STM32F103RCT6 and F411 microcontroller, the display effect is the same

video.3.mp4

Here is my test code
void loop(void)
{

// create foreground colors
uint16_t col[] = {
    dmd.Color888(255,0, 0), // red

};
uint16_t bg = 0;  // background - black
int col_cnt = 3;   // color count

// text
char s[] = "hello 1122334455";
// transcode message to UTF for use with GFX fonts
char k[30];

utf8_rus(k, (const unsigned char*)s);
char* m = s;
// select standard font
dmd.selectFont(&UkrRusArial_F);

// set text foreground and background colors
dmd.setTextColor(col[0], bg);

// shift steps in pixels for running text (positive - shift right, negative - left)
int8_t step[] = { -1,-1,-1,-1 };
// running text shift interval
uint16_t interval = 10;

long prev_step = millis();
uint8_t col_ptr = 0;
uint8_t i = 0, b = 0;
uint8_t test = 255;
uint8_t test_cnt = 4;
dmd.setBrightness(100);
int x=dmd.width() - 1;
while (1) {
    if ((millis() - prev_step) > interval) {
      prev_step = millis();  // moved to the start of the loop to prevent "scroll not smooth" issue
      x--;
      if(x<-1*dmd.stringWidth(m))
      {
        x= dmd.width() - 1;
      }

    }
      dmd.drawMarqueeX(m, x, 12);
      dmd.swapBuffers(true);
    
}

}

[ShiPC123]

1.mp4

[board707]

Hi
Could you clarify an issue? I didn't catch the problem from the video.

[ShiPC123]

Hello, maybe can't see the effect from the inside of the camera, but to the naked eye, can see how Carton feels. The rolling is not smooth

[ShiPC123]

How can I improve the flow of the roll

[board707]

Honesty, I don't see any distortions :)
I have try it at home.

By anyway, try to increase a scrolling interval:
uint16_t interval = 10;
The 10 mS is probably too tight for the task.

[ShiPC123]

Thanks, I will try to re-shoot the video tomorrow, and I feel that the shadow will appear when I scroll

[ShiPC123]

Is there any relevant document that can explain the function, such as dmd.drawMarqueeX? I wonder if I didn't clear the screen or didn't call some functions, which caused the scrolling to have residual shadows

[board707]

Read the library Wiki
The brief explanation of the functions: DMD_STM32 Reference

[Suresh6060]

I have used this library with very good success. It is true , I had to struggle a bit to get it running though.

There are some quirks that I could not understand fully. May be it is timing or memory management issue.

In my case , I had to declare the variable m[] as a global variable. This introduced new problems with unknown characters or characters of the previous scrolls added to the new scroll. Technically this should not happen. But that was the case. To solve the issue I add a for loop and re-assigned m[]=NULL , resetting the variable , before using it again . BTW i was dynamically populating m[] and not sending a static text to drawMarquee ().

The variable interval practically determines the speed to scroll.

I this this library works in two stage. drawMarquee had to be initially setup as it initializing with stepmarquivee etc. don't use swapbuffers() here.

The second stage is used to subsequent repeat, reversal, vertical etc.

This is a little bit different from how DMD is implemented in esp32 etc.

I might be wrong, but this is what I understood and used.

At one point I had the slowing issue and tested outputing the actual time each section of code takes to finish and tweeked the code. Hope you know C is an admant , stuborn and unforgiving langauge. memory management has to very precise.

[board707]

I had to declare the variable m[] as a global variable. This introduced new problems with unknown characters or characters of the previous scrolls added to the new scroll. Technically this should not happen. But that was the case.

Did you forget to add the string terminator at the end of the line?

For this and another issues, please show the code that demonstrate the problem.