Initial Pause When Not Clearing in P2D and P3D Renderers

[processing-bot]

Created by: JeremyEastham

Description

When rendering with either the P2D or P3D renderers, there is a noticeable pause on the first frame of the sketch if background is not called. Normally this pause is not very long, but this pause becomes more noticeable at higher resolutions and if multiple PGraphics objects are used as buffers.

Minimal Code to Reproduce

void setup()
{
  fullScreen( P2D );
}

void draw()
{
  fill( frameCount % 2 * 255 ); //Flash every odd frame
  rect( 0, 0, width, height );
  //A workaround would be to replace the above lines with background(...);
}

Testing Code

//Testing variables
boolean callBackground = false; //Toggle bug
boolean useBuffers = false;
int numBuffers = 2;

//Public variables
PGraphics[] buffers;
long startTime; //Time when setup returns

void setup()
{
  fullScreen( P2D ); //Also works with P3D
  background( 0 );
  noStroke();
  fill( 0 );
  if( useBuffers )
  {
    //Allocate buffers
    buffers = new PGraphics[numBuffers];
    for( int i = 0; i < numBuffers; i++ )
      buffers[i] = createGraphics( width, height, P2D );
  }
  //Record time before first frame
  startTime = millis();
}

void draw()
{
  if( frameCount == 1 ) //1st Frame
  {
    if( callBackground )
      background( 0 );
    else
      rect( 0, 0, width, height );
    if( useBuffers )
      for( PGraphics buffer : buffers )
      {
        buffer.beginDraw();
        if( callBackground )
          buffer.background( 0 );
        else
          buffer.rect( 0, 0, width, height );
        buffer.endDraw();
      }
  }
  
  if( frameCount == 2 ) //2nd Frame
  {
    long elapsed = millis() - startTime;
    fill( 255 );
    text( "2nd frame took " + elapsed + "ms", width / 2, height / 2 );
    println( elapsed + "ms" );
  }
}

With the testing code above, the amount of time to render the 2nd frame is ~40ms when callBackground is false and ~4000ms when callBackground is true (without buffers). Adding buffers increases the time by multiple seconds.

Your Environment

• Processing version: 3.5.4 (have not tested with Processing 4)
• Operating System and OS version: Windows 10.0.19043 Build 19043
• Other information: Intel Core i5-10210U with Intel UHD Graphics 620

[processing-bot]

Created by: reiaaoyama

I tried your code on MacBook Air 2014, BigSur 11.6.4 + Processing 4.0 (beta) 1

• CPU: core i5 1.4GHz
• Graphic: Intel HD Graphic
• Screen: 1366x768

Result:

• 273 ms with callBackground = false;
• 37 ms with callBackground = true;

I check the (implementation of background() which calls backgroundImpl( )]( https://github.com/processing/processing/blob/a6e0e227a948e7e2dc042c04504d6f5b8cf0c1a6/core/src/processing/core/PGraphics.java#L7498) and don't see anything that should make calling background() makes it faster to draw the 2nd frame.