The WM_CREATE message arrives whenever a new window is created. Since usually a window is created only once, the one-time activity that is to be carried out in a program is usually done in OnCreate( ) handler. In our program to make the ball move we need to display it at different places at different times. To do this it would be necessary to blit the ball image several times. However, we need to load the image only once. As this is a one-time activity it has been done in the handler function OnCreate( ).
You are already familiar with the steps involved in preparing the image for blitting—loading the bitmap, creating a memory DC, making it compatible with screen DC and selecting the bitmap in the memory DC.
Apart from preparing the image for blitting we have also done some intialialisations like setting up values in some variables to indicate the initial position of the ball. We have also called the SetTimer( ) function. This function tells Windows to post a message WM_TIMER into the message queue of our application every 50 milliseconds.
You are already familiar with the steps involved in preparing the image for blitting—loading the bitmap, creating a memory DC, making it compatible with screen DC and selecting the bitmap in the memory DC.
Apart from preparing the image for blitting we have also done some intialialisations like setting up values in some variables to indicate the initial position of the ball. We have also called the SetTimer( ) function. This function tells Windows to post a message WM_TIMER into the message queue of our application every 50 milliseconds.
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