Initial Pause When Not Clearing in P2D and P3D Renderers

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

从提供的最小示例和测试示例开始，比较 P2D 和 P3D 在有无 background() 以及使用 PGraphics 缓冲区时的首帧时序。跟踪首帧涉及的 renderer 初始化和清除行为；当不调用 background() 时，测试示例不再出现报告中的数秒暂停，即表示完成。