How to work around blinking display when with SPI tft display

i playing using spi tft display little project displays data.

i'm using adafruit libraries

code: [select]

#include <adafruit_gfx.h>    // core graphics library
#include <adafruit_st7735.h> // hardware-specific library


i've wired fast display find have how erase previous data displayed before updating it.  @ first did clear screen with

code: [select]

tft.fillscreen(st7735_black);
before showing new data (text rotated)
but blinking awful

then tried drawing black rectange on area of text with

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tft.fillrect(0, 30, 200, 60, st7735_black);

and it's tiny bit better. there must better way. can't wonder if it's overall structure of code real issue.

here's full code

code: [select]

#define cs   10
#define dc   9
#define rst  8  // can connect arduino reset

#define trigger_pin  7  // arduino pin tied trigger pin on ultrasonic sensor.
#define echo_pin     6  // arduino pin tied echo pin on ultrasonic sensor.
#define max_distance 600 // maximum distance want ping (in centimeters). maximum sensor distance rated @ 400-500cm.

#include <adafruit_gfx.h>    // core graphics library
#include <adafruit_st7735.h> // hardware-specific library
#include <spi.h>
#include <newping.h>
//#include <stdio.h>

newping sonar(trigger_pin, echo_pin, max_distance);

#if defined(__sam3x8e__)
    #undef __flashstringhelper::f(string_literal)
    #define f(string_literal) string_literal
#endif

adafruit_st7735 tft = adafruit_st7735(cs, dc, rst);

void setup(void){
   serial.begin(115200);
  tft.initr(initr_blacktab);
  tft.settextwrap(false); // allow text run off right edge
  tft.fillscreen(st7735_black);
  tft.setrotation(1);
 
}
void loop(void) {
 
int totalping=0;                      // wait 50ms between pings (about 20 pings/sec). 29ms should shortest delay between pings.
  unsigned int us;
(int i=0;i<=4;i++){
  = sonar.ping(); // send ping, ping time in microseconds (us).
  serial.print("reading");
  serial.print(i);
  serial.print(":");
  serial.println(us/us_roundtrip_in);
  totalping=totalping+us;
  delay(30);
  }
  tft.fillrect(0, 30, 200, 60, st7735_black);
  us=totalping/5;
  int r;
  int f;
  int i;
  int remainder;
   
   tft.settextsize(1);
   tft.setcursor(0,100);
   tft.print("rangefinder v 0.1");
   tft.settextcolor(st7735_yellow);
   tft.settextsize(6);
   tft.setcursor(0, 30);
   r=us/us_roundtrip_in;
   serial.println(r);
   remainder=r%12;
   f=(r-remainder)/12;
  tft.print(f); // convert ping time distance in cm , print result (0 = outside set distance range)
  tft.print(":");
  tft.print(remainder);
  //delay(50);
 
}

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