Tower Defense Tutorial - Brackeys - Ep. 23

March 2, 2019

Tower Defense Tutorial

Episode 23 – Enemy Health Bars

Youtube - How to make a Tower Defense Game (E23 HEALTH BARS) - Unity Tutorial
By: Brackeys
Ep. 23

In this tutorial we created health bars for the enemies.

We began by creating the foundation for the UI asset. We created a new World Space canvas, added a child UI Image object as our health background, then childed a UI image to that that would be our actual health bar. The BG was given a transparent black color, while the health bar was a fully opaque light green.

We then childed this full group of UI assets to our Enemy prefab. The position needed fixed when this was applied, and the scaling reset so I had to reset that manually as well. This created a health bar that would follow our enemies now. We would need a bit of a tracking script if our enemies rotated (so the health bar would not), but currently the enemies don’t rotate at all so this is not necessary.

To make our health bar actually do something, we started by dragging in a white square image to the source image of the health bar UI image, which was created for the tutorial. It was just a simple 2 x 2 white square. We then changed the Image Type to Filled, and selected the Fill Method “Horizontal”. This allows us to control how much of the image is “filled” horizontally, between 0 and 1 (0 – 100%). This has a very similar effect to what I usually script for health bars which is just a scale multiplier between 1 and 0 tied to the x scale of an object with the anchor point located all the way on the left/right. Either way, this still needs to be tied into health scripts.

Our fill amount for this health bar image needs to be between 0 and 1, so we need to represent our current enemy health as some fraction of our enemy max health. This is easy enough to do by simply holding a value for the max health and dividing the current health by the max health.

PROBLEMS

Bug

I found a bug where some of the turrets I was placing could not be upgraded. They were base turrets but when I selected them it already said they were “Maxed Out” and I could not upgrade them. It was only a select few turrets, and I realized they were in locations where I had an upgraded turret previously and sold it to make room for a new turret.

I believe this bug is simply caused by the fact that the state of upgraded is tied to the node location, so when we upgrade and then sell, the upgrade state is not being reset. That should be a simple fix of resetting the upgrade state when the Sell method is invoked.

Solved

This appeared to be the case as the bug hasn’t come back since I simply added a line to set the isUpgraded bool to false in the Sell method of the Node script.

SUMMARY

  • Another way to create health bars: under the Image (script) component; select image type Filled, and choose Fill Method “Horizontal”

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