The Move Path tool (Image: Video > Move Path) is the main interface for GAP. As you learned in Method Three: Moving Along a Path, you first need to follow these steps:

If you haven’t set up the environment properly before opening the Move Path tool, the tool complains and refuses to work. Note that you can use an existing multi-image animation as the background, rather than creating one as we’ve done. In this case, simply open the source animation (Step 1 ) and then open the background animation, and you’re ready to open the Move Path tool.

The Move Path tool adds layers from the source image to a sequence of frames in the target animation. You define how layers are added to the frames by modifying several parameters. Basically, you define positions (i.e., relative locations) in the target animation; for each position, define these values for the following parameters:

Figure 6-44. The initial landscape

If the source image has an active selection, however, you can choose to add just the selection to the new animation.

You can use the Move Path tool to build an animation with several scenes by building a complex path for the layers in the successive frames and applying changes to only a subset of the frames that correspond to a specific scene.

Finally, and this point is important, to add several layers to the target frames, apply the Move Path tool multiple times—once for each layer.

We’ll walk you through two new examples to demonstrate some nifty things this tool can do.

First, we make an animation that simulates somebody looking at a scene through binoculars and moving the binoculars in search of a target. The scene is a village surrounded by mountains, as shown in Figure 6-44.

We add the binoculars as a new layer that’s completely black except for two overlapping circles that are transparent. Here are the steps to create the binoculars:

Figure 6-45. Adding the binoculars

Figure 6-46. Moving the binoculars

The result should look like Figure 6-45.

In our animation, we move the binoculars around the landscape. But both layers are currently the same size, so as the binoculars move, the black won’t fully cover the background, resulting in something like Figure 6-46. To avoid this, we need to enlarge the top layer to cover the landscape.

Figure 6-47. Enlarging the upper layer

Select Image: Layer > Layer Boundary Size, increase the size in both directions, and center the canvas around the enlarged layer, as shown in Figure 6-47. Then make this entire layer black, except for the binocular window. Because this layer is now larger than the canvas, this step is somewhat tricky. Here’s one way to do it:

Because we enlarged the image, we need to crop it at the end of the process.

Now create a new folder for the animation; call it Binoculars. Drag the background layer thumbnail from the Layers dialog to the Toolbox, and save the image as bin-0001.xcf in the new folder Binoculars.

Duplicate this frame 59 times, using Image: Video > Duplicate Frames. The animation now has 60 frames. We use a path to move the binoculars around the landscape. Choose the Path tool in the Toolbox () and click to add points to the background image you just saved, as shown in Figure 6-48.

Figure 6-48. The binocular path across the landscape

Figure 6-49. Importing the path as a sequence of controlpoints

Select the Move Path tool (Image: Video > Move Path. . . ). In the dialog, check that the selected layer is the top layer of the source image, which appears mostly black in the thumbnail. Choose None for the STEPMODE and Center for the HANDLE.

Click the GRAB PATH button in the EDIT CONTROLPOINTS area of the dialog to import the path we just built as a sequence of control-points, which are equally placed across the 60 frames. Then the dialog should look similar to Figure 6-49.

The GAP plug-ins lack the capability to undo, so check the animation you just built by clicking ANIM PREVIEW. If everything is correct, click OK to generate the final animation. Discard the multilayer image that was created for the preview.

Although it did serve as a basic introduction to using paths with the Move Path tool, the animation we just created isn’t very realistic. If you are looking through binoculars, it’s the landscape that appears to be moving, not you.

If you closed it, open the binocular animation that you just made. Create a new folder for the next version of the animation and then create a new blank image that’s much smaller than the landscape in the source image. For this example, we create a 521 × 338 image, and our landscape image is 1042×676. Save this image into the new folder with name bin-0001.xcf, and duplicate it 59 times with Image: Video > Duplicate Frames.

Open the Move Path tool dialog (Image: Video > Move Path). Choose the landscape layer of the previous animation as the source layer (top left of the dialog), None for STEPMODE (below SOURCE IMAGE/LAYER), and Center for HANDLE (to the right of STEPMODE), and check INSTANT APPLY at the bottom of the dialog. This time, let’s build the path within the Move Path tool dialog by clicking in the preview to place points. Click ADD POINT and then click in the preview to add a new point. If you click close to an existing point in the preview, you end up moving that point rather than adding a new one, so click the last point and drag it to add a new one instead. Note that the source image moves around as you place the points. Our result is shown in Figure 6-50.

Before finalizing this animation, check the CLIP TO FRAME checkbox and then click OK. GIMP processes for a while as it builds the first part of the animation, with the landscape moving in the smaller image. You can test the result by selecting Image: Video > Playback.

Figure 6-50. Creating the path by hand

Figure 6-51. Placing the second layer

Now place the binoculars above these landscape frames. Use a layer mask. Add the mask as a new layer to all the frames with the Move Path tool again. Figure 6-51 shows the settings we used. The binocular layer is chosen as source layer and placed in the center of the image.

Simply click OK to get the new animation. Each frame contains three layers—from top to bottom: the binocular image, the landscape, and a white background. We want to merge the topmost layer with the background and use the resulting layer as a mask for the landscape layer. This reduces the number of layers and demonstrates the Image: Video > Frames Modify tool at the same time.

Figure 6-52. Lowering the topmost layer

Figure 6-53. Merging the two bottom layers

The Frames Modify tool is handy for modifying a set of layers across all the frames in a multi-image animation. The dialog appears in Figure 6-52, showing our first selections. Click the FUNCTION menu (at the top of the dialog) and select LAYER STACKPOSITION >LOWER LAYER(S). Leave PATTERN IS A LIST OF LAYER STACK NUMBERS checked, and enter 0 for LAYER PATTERN. Click OK.

Figure 6-54. Using the bottom layer as a layer mask

Next we merge the two bottom layers. Select the Modify Frames tool again, and this time choose the settings shown in Figure 6-53. Because the layers are numbered from top to bottom beginning at 0, the layer pattern is “1 2.” The resulting composite layer is named Background.

The final step is shown in Figure 6-54. The bottom layer acts as a mask for the landscape layer.