Add support for graphics clipping

[ImpulseAdventure]

Drawing inside clipping regions

This enhancement adds setClipRect() which defines the clipping region used for the drawing primitives that follow (per #769 ).

• setClipRect(int32_t x, int32_t y, int32_t w, int32_t h)
• This can be useful when only a portion of an image needs to be updated; speeding up the redraw in the process

Supported functions

I tried to update all of the APIs that previously performed screen region clipping to support the custom clipping region. This means that the following APIs now support the clipping region:

• pushImage(): all variants
• drawChar(): the default function
• drawPixel()
• drawFastVLine()
• drawFastHLine()
• fillRect()

Functions not updated

• Sprite operations were not touched
• DMA operations were not touched
• I have not touched the drawChar() UNICODE variant

Notes

• The clipping region works with dynamic setRotation(), and is reset accordingly
• I would expect this enhancement to have no negative performance impact (it should only improve performance)
• If a user has set a custom clipping region, it can be reset to the default by assigning the entire display: tft.setClipRect(0,0,tft.width(),tft.height());

Testing

• Testing of this revision on a number of example sketches so far appears to show it to be working.
• Attached is a modified version of TFT_graphicstest_one_lib that demonstrates the result of a custom clipping region. You can un/comment the TEST_CLIP macro to observe the changes.
• TFT_graphicstest_one_lib-clip2.zip

Thanks for your time

[Bodmer]

See "viewport" branch of TFT_eSPI.