RasterLayer: Properly handle GUI updates when multiple canvas are displayed #59444
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This will be used in the next commits to store the min-max values of a raster layer and report them to the main canvas.
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`QgsRasterLayer` updates the GUI (the renderer widget and the legend) when the rendered values are updated. This does not work when multiple canvas are displayed because each canvas causes a renderer update. This issue is fixed by removing the GUI update from the raster layer code. With this change, when the rendered values are updated, these statistics are propagated to the canvas by the use of a `QgsRenderedItemDetails`: `QgsRenderedCalculatedResults`. Then, only the main canvas is notified of this change and updates the GUI accordingly.
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Description
This fixes an issue mentioned by @nyalldawson in qgis/QGIS-Enhancement-Proposals#273
This occurs when the Min/Max settings is set in the renderer and multiple canvas are displayed. Indeed, in that case
QgsRasterLayerupdates the GUI (the renderer widget and the legend) multiple times when the rendered values are updated because each canvas causes a renderer update.This issue is fixed by removing the GUI update from the raster layer code. With this change, when the rendered values are updated, these statistics (min-max) are propagated to the canvas by the use of a
QgsRenderedItemDetails:QgsRenderedCalculatedResults. Then, only the main canvas is notified of this change and updates the GUI accordingly.