Reference » Dictionary » Painting functions

Painting functions

Description

MWindow functions that define graphical content inside the window.

Details

The painting functions are normally used inside OnPaint (see Paint) to define the entire visual appearance of the window, although they can be used outside of OnPaint as well. Recognizing these functions is easy - they all contain the word "draw" or "fill" in their names, and they are the only MWindow functions with such distinction.

All the painting functions are subject to a coordinate and dimension transformation, defined by MWindow::setDrawTransform. By default, all the coordinates are relative to the top-left corner of the window (regardless of the MWindow::RTL property) and all the sizes are in physical pixels. However, a transform can change the origin point and scaling factors. See MWindow::setDrawTransform and MTransform for more information.

Only the painting functions that are used inside OnPaint have a "permanent" effect - the results of painting outside of OnPaint are erased the next time the window is repainted, which can happen at any moment for various reasons, some of which are beyond the app's control. Therefore, it is not recommended to use the painting functions outside of OnPaint, except for the MWindow::calcDrawTextSize revealer.

During OnPaint, pixels inside the window can be invalid or valid (see MWindow::repaint). The painting functions affect only the invalid pixels (whose content is undefined - that is why they need to be repainted). The content of the valid pixels remains unchanged even if a drawing function is used on it. Outside of OnPaint all pixels are affected by the painting functions.

Regardless of whether the functions are used inside or outside OnPaint, they do not affect anything outside of the window's canvas, i.e. they are clipped by the window's boundaries and by all the windows, whose rectangles intersect with this window (e.g. children or siblings with higher z-order). The only exception is the screen window, whose painting functions draw directly on the screen, on top of all the windows.

These are all the painting functions in MWindow:

Drawing (outline painting):

Filled shape painting:

Complex shapes:

Special:

Also, the following properties affect the graphical content, even though they are not painting functions themselves and should not be used during OnPaint:

Flushing:

The painting functions do not affect the window right away, but are kept in an internal buffer until it is flushed. In other words, a painted shape does not appear on the screen after calling a painting function. The graphic content appears all at once when the paint buffer is flushed. This buffering is needed to prevent the annoying flickering effect, which occurs if different shapes are painted on top of each other (which is practically unavoidable in most situations).

The flushing occurs automatically after each message processing and also before mcPaint processing (so during Paint the buffer is flushed before and after the handler). Also, all the buffers (for all windows) are flushed before suspending the main thread as a result of MApp::sleep. This actually means that the graphics can be flushed manually by calling MApp::sleep(0), but that is rarely necessary. The flushing before sleep is useful for animated graphics, where sleep is used for properly timing the animation.

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Page last updated on August 10th, 2014.