Double Buffering - mchpgfx/legato.docs GitHub Wiki

Double Buffering: Legato vs Aria

Aria: Single Buffer

The draw algorithms can paint pixels directly into the display frame buffer in Aria Graphics Library. This the most simplistic method and requires the least amount of memory. The drawback is visually observable screen tearing, since the display controller has to refresh the display at a much higher rate than the pixels are updated by the draw algorithms.

Aria Single Buffer Draw

Aria: Double Buffer

Screen tearing can be eliminated by using two frame buffers. This scheme doubles the memory requirement.

In the DRAW phase, the draw algorithms update the back/write buffer. The display controller reads from front/read buffer.

Aria Double Buffer Draw Phase

In the SWAP phase, the buffers roles are swapped at V-BLANK. The front/read buffer is now the back/write buffer for the draw algorithms and the display controller reads from the former back/write buffer, now the front/read buffer.

Aria Double Buffer Swap Phase

In the SYNC phase, the draw algorithm applies the same updates to the former front/read buffer such that the content from both buffers are in-sync.

Aria Double Buffer Sync Phase

Legato: Virtual Double Buffer

To help minimize screen tearing, Legato's draw algorithms paint to a tiny scratch/back buffer. The scratch/back buffer is then copied into the frame buffer using fast bulk transfer techniques. The size of the scratch/back buffer is configurable in the MGS Harmony Composer. Depending on the performance of the graphics hardware technology and the GUI design requirement, this adjustment may be enough to eliminate screen tearing. This 'virtual double buffering' scheme can use less memory than double buffering.

Legato Virtual Double Buffer Draw

Legato: Double Buffer

For absolute elimination of screen tearing, Legato can be configured to full double buffering.

In the DRAW phase, the scratch/back buffer(s) are copied to the back/write frame buffer. The display controller reads from the front/read buffer. The display controller driver keeps track of the rectangular sections of the frame buffer that were updated.

Legato Double Buffer Draw Phase

In the SWAP phase, similar to Aria, the buffers roles are swapped at V-BLANK. The front/read buffer is now the back/write buffer for the draw algorithms and the display controller reads from the former back/write buffer, now the front/read buffer.

Legato Double Buffer Swap Phase

In the SYNC phase, the display controller driver re-applies the updated sections of the frame from the Front/Read Buffer to the Back/Write Buffer to keep both buffers in-sync.

Legato Double Buffer Sync Phase

If you are new to MPLAB® Harmony, you should probably start with these tutorials:

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