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Read the Animation Variable Values

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Each time your application paints, it should read the current values of the animation variables that represent the visual characteristics to be animated.

Overview

When drawing a frame, an application can use the IUIAnimationVariable::GetValue or IUIAnimationVariable::GetIntegerValue method to request the values of any animation variables that will affect visuals within the frame. It is possible to clip an animation variable to a range of values (SetLowerBound and SetUpperBound), and to request its value be rounded to an integer using a specified rounding scheme (SetRoundingMode).

Instead of reading the values of all variables for every frame, an application can use the IUIAnimationVariable::SetVariableChangeHandler or IUIAnimationVariable::SetVariableIntegerChangeHandler method to register one or more variable change handlers to receive notifications only when there is a change to the variables' value (IUIAnimationVariableChangeHandler::OnValueChanged) or rounded value (IUIAnimationVariableIntegerChangeHandler::OnIntegerValueChanged). To identify the variables passed to variable change handlers, an application can apply tags to variables using the IUIAnimationVariable::SetTag method. These are object (IUnknown*), integer pairs that are interpreted by the application.

Example Code

The following example code is taken from Thumbnail.cpp in the Windows Animation sample Grid Layout; see the CMainWindow::Render method. It uses the GetValue method to read the values as floating-point values.

// Get the x-coordinate and y-coordinate animation variable values

DOUBLE x=0;
hr = m_pAnimationVariableX->GetValue(&x);
if (SUCCEEDED(hr))
{
    DOUBLE y=0;
    hr = m_pAnimationVariableY->GetValue(&y);
    if (SUCCEEDED(hr))
    {
        // Draw the object

        ...

    }
}

The following example code is taken from MainWindow.cpp in the Windows Animation sample Timer-Driven Animation; see the CMainWindow::DrawBackground method. It uses the GetIntegerValue method to read the values as integer values.

// Get the RGB animation variable values

INT32 red;
HRESULT hr = m_pAnimationVariableRed->GetIntegerValue(
    &red
    );
if (SUCCEEDED(hr))
{
    INT32 green;
    hr = m_pAnimationVariableGreen->GetIntegerValue(
        &green
        );
    if (SUCCEEDED(hr))
    {
        INT32 blue;
        hr = m_pAnimationVariableBlue->GetIntegerValue(
            &blue
            );
        if (SUCCEEDED(hr))
        {
            // Set the RGB of the background brush to the new animated value

            ...
                
            // Paint the background

            ...

        }
    }

    ...

}

Previous Step

Before starting this step, you should have completed this step: Update the Animation Manager and Draw Frames.

Next Step

After completing this step, the next step is: Create a Storyboard and Add Transitions.

IUIAnimationVariable::GetIntegerValue

IUIAnimationVariable::GetValue

Windows Animation Overview