Before we start, let's first explain the homework after the last class, which is an animation with two objects moving together. The so-called two objects are actually two layers. Draw a square and a circle respectively, then copy one frame and move the positions of the layers relatively. It's not technically difficult. 
But please pay attention to our sample animation. The circle in it does not move at the beginning, but starts after a period of lag. This means that in the first few frames only the square layer needs to be moved, not the circle layer. After the square has moved a few frames before you start moving the circle, the animation palette will look like the image below. Click the red arrow to open the palette options and set the size of the frame thumbnail yourself. at the green arrow
It is the frame step button. Click to play one frame at a time.
It plays the previous frame.
button returns to the starting frame.
We arranged this example to tell everyone that a more complex animation is often composed of many objects, and these objects may not all move (such as move) together. For example, when making an animation of one object hitting another object, the hit object should remain motionless until the hitting object comes into contact.
Previously, we made displacement animations, which used the movement of layers. In addition, you can also create animation by setting different layer transparency. I believe everyone can guess the production method, which is to change the partial transparency value in the layer palette in different frames. Now create a new 100×100 image, create a new layer and draw a square. Then copy 5 frames at once, and you will see that all 6 frames have the same content. Change the dwell time of all frames to 0.1 seconds, as shown in the left picture below.
Then select frame 2 and change the opacity of the square layer to 80% in the layers palette, then 60% for frame 3, and so on until frame 6 is 0%. The effect is similar to the one shown on the right below. At this time, when playing, you will see the effect of the blocks gradually fading out. It should be noted that through
The button to hide the layer is equivalent to setting the opacity to 0%.
A big difference in this production is that we changed the original method of copying one frame and setting it immediately, and then copying another frame after setting it. This time, all the frames are copied at once, and then the frames are selected for settings. This is also a production method.
During the operation, it is not difficult to find that the opacity in the layer palette will return to 100% when another frame is selected. This illustrates the fact that changing the opacity of one frame does not affect the other frames. Imagine again, if we use this method to create the initial block movement, what will happen when we select the next frame after moving the layer in the previous frame?
Obviously, we're going to see the squares come back to square one. And if the layer position setting at this time does not follow the trajectory of the previous frame, a smooth movement effect will not be achieved. Therefore, this method of pre-building all frames and then modifying them is not suitable for displacement animation, nor is it suitable for other animations. It is only used when you need to animate in a specified number of frames.
Now that we have mastered two settings that can produce animation effects, one is the layer position, and the other is the layer opacity. Now we can use both to create an animation that both moves and fades. This can be modified based on the simple fade just now. That is to say, use a simple method, select a frame and then move it a little, and so on.
But we need an effect of moving from the left end to the right end, which means that the starting position of the block must be at the left end, but now the blocks in all frames are in the middle. What should we do? Since "all frames" are in the middle, let's make "all frames" go to the left. Select all the frames in the animation palette, use the move tool to move the layer to the far left, and you will see that the position of the squares in all frames has changed.
There is another way. The entire animation process can be seen as a relationship between cause and effect. If you delete a layer on the first frame, it will no longer exist in all subsequent frames. Therefore , in Photoshop animation settings, the first frame is relatively special. Now select the first frame and make sure "Spread Frame 1" is enabled in the Layers palette, as shown by the red arrow in the left image below. Then move the layer, and you will find that the blocks in all frames have moved uniformly, as shown in the right picture below. If "Propagate Frame 1" is invalid, only the block position in frame 1 will be changed.
Both methods have their own pros and cons. "Propagating frame 1" actually means "propagating frame 1", which means propagating the changes in frame 1 to all frames. It can easily change the settings of certain objects in the entire animation. And The method of selecting all frames will be a little troublesome when the number of frames is large, but it can be derived from the method of "selecting certain frames". For example, when you only need to change the first 3 frames, you can select the first 3 frames together and set them. Certainly.
It should be noted that "Propagate Frame 1" is still effective even if a different layer position is originally set for each frame. The effect is equivalent to the coordinates in all frames being offset according to the first frame.
Let’s talk about the issue of selecting multiple frames again. We already know that if you want to select the first 4 frames, you can first select frame 1 and then hold down the SHIFT key and then click on frame 4, or the opposite can be done. But if you want to select discontinuous frames, such as frame 1, frame 3, and frame 4, you can first select frame 1 to frame 4 according to the previous method, and then hold down the CTRL key and click frame 2 to subtract the selected frame 2. . Repeat the operation once to add selection frame 2. If you want to select individual frames that are far away, such as frame 2, frame 11, frame 17, and frame 27, you can select any one of them individually first, and then hold down CTRL to add and select other frames.
After moving the blocks in all frames to the left, all you need to do is to set the position of the blocks frame by frame, that is, select the 2nd frame to move a little, and the 3rd frame to move a little. Of course, there is a problem we have already mentioned, that is, it is difficult to ensure smooth movement. We have learned in Photoshop that when selecting the move tool, you can use the arrow keys on the keyboard to move the layer 1 pixel at a time, and use the SHIFT key to move it over long distances.
Now let's select frame 2 and move it with SHIFT+right arrow key. Then select frame 3. Since the block in this frame has returned to the starting point, you need to SHIFT + the right arrow key twice. In frame 4, it is 3 times, and so on. The settings are similar to the one shown below. The square has disappeared in frame 6, so no setting is required.
Although the method of using the direction keys to move can ensure the consistency of the trajectory, its limitation is also obvious, that is, it is only suitable for making trajectories such as horizontal, vertical or 45-degree angles. What if we need a more random movement trajectory (such as an arc) but want to maintain smoothness? Of course, everyone will say that if you use the "copy frames and move layers" method from the beginning, you will not have the current troubles, but please don't forget that it is common to modify the motion trajectory. So think carefully about how to operate it.