Screen Tearing Simulation & Educational Demo
Because modern desktop compositors (Windows DWM, macOS Quartz, Linux Wayland) enforce VSync at the window level, true screen tearing cannot occur inside a windowed browser. This tool provides an accurate visual simulation of buffer mismatches.
- Adjust simulated frame rate above and below simulated refresh rate to see horizontal shear lines.
- Observe how tearing occurs when the front buffer is swapped mid-scanout of the display.
- Understand why G-Sync, FreeSync, and VSync eliminate tearing artifacts in native gaming environments.
Screen tearing happens when the graphics card flips the front and back display buffers in video memory while the physical monitor is actively scanning electron beams or digital rows down the panel. The top half of the screen displays the previous frame, while the bottom half displays the new frame, resulting in a fractured horizontal shear line.
What This Test Checks
- Mechanics of screen tearing: horizontal shear line splitting consecutive video frames.
- Mid-scanout front buffer swapping in GPU video memory.
- Why desktop compositors (Windows DWM, macOS Quartz) prevent windowed tearing.
- How VSync and Variable Refresh Rate (G-Sync / FreeSync) eliminate tearing.
How to Perform the Test
- Observe the horizontal tear line cutting through the moving high-contrast bars.
- Adjust the Scanout Tear Position slider to move the tear line vertically up and down.
- Toggle "Enable Tear Line Simulation" on and off to compare torn vs clean motion.
- Read the educational guide below explaining why modern browsers enforce VSync.
What to Look For
- Tear line: A sharp horizontal boundary where top and bottom images are misaligned.
- Shear offset: Fast movement exaggerates the horizontal distance between torn segments.
- Single vs Multiple tears: When framerate is multiples of refresh rate, multiple tears can appear.
Common Display Problems & Diagnostic Guidance
Why Can’t True Tearing Happen Inside a Web Browser?
Modern desktop operating systems composite all windowed applications using a triple-buffered compositor with forced VSync. Even with VSync turned off in GPU control panels, windowed browsers never tear physically.
The Trade-off: VSync vs Input Lag
Traditional VSync completely eliminates tearing by waiting for the monitor’s vertical blanking interval, but adds 1–2 frames of input latency. VRR solves both problems simultaneously.
Frequently Asked Questions
Is this actual tearing or a simulation?
This is strictly an educational simulation. We label it clearly because honest representation of browser capabilities is a core ScreenCheck principle.
How does G-Sync / FreeSync prevent tearing without lag?
Instead of forcing the GPU to wait for the monitor’s clock, VRR forces the monitor to wait for the GPU: the monitor refreshes immediately when a new frame is completed.