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ENEMY_SPRITES.md

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How enemey sprites work

Filenames

Single-animation pattern

Image filenames follow a specific pattern:

TROOB1

Where:

  • TROO is the PREFIX for the Imp.
  • B is the second walking/idle FRAME.
  • 1 is the front-facing ANGLE.

Pattern:

${PREFIX}${FRAME}${ANGLE}

Frames and animations

A FRAME is always a letter. The letters used to define all the frames of a single enemey are consecutive (from A to Z, without any gap).

When grouped, these frames make an animation. Each enemy has its own set of animations, such as walking, range attack, melee attack, pain, death, gib death, etc.

Each enemy animation can consist of a variable number of frames, which makes it hard to predict which letter corresponds to which animation.

For example, here is the breakdown of the animations of the Shotgun Guy (where the PREFIX is SPOS):

  • Walking: A-D (4 frames).
  • Range Attack: E-F (2 frames).
  • Death: G-L (6 frames).
  • Gib Death: M-U (9 frames).

Compare to the breakdown of the animations of the Spider Mastermind (where the PREFIX is SPID):

  • Walking: A-F (6 frames).
  • Range Attack: G-H (2 frames).
  • Pain: I (1 frame)
  • Death: J-S (6 frames).

The G FRAME of SPOS is part of its death animation, whereas the same FRAME for SPID is part of the range attack animation.

Enemies also have an idle animation, which is programatically defined as a loop of the A and B frames (ie, the two first frames of the walk animation).

Note that death animations do not support different angles, which is represented by the usage of 0 (zero) in the filename of these animations. The 0 ANGLE is always front-facing.

The number of frames as well as the letter of the starting and ending frame of each animation should be defined in the JSON object where enemies are listed.

Prefix

The PREFIX is always 4-character long. It is used to identify all the animations of a specific enemey.

The PREFIX can include numbers, which can be a little confusing:

BOS2E3

The example above represents the E FRAME of the BOS2 enemy (also known as the Hell Knight). In this case, the 2 in BOS2 is used to differentiate this animation from BOSSE3, which is a FRAME belonging to the Baron of Hell.

Mirrored pattern

Mirrored angles

Sometimes, the same image is used for two different ANGLE values:

${PREFIX}${FRAME}${ANGLE1}${FRAME}${ANGLE2}

Example:

TROOA2A8

In this case, the PREFIX of the animation is TROO (the Imp). The name of the file tells us that this image is used for both ANGLE 2 (front-facing left) and 8 (front-facing right) of FRAME A (first walk animation).

Filenames which follow this convention are automatically mirrored when displaying ANGLE2.

Sprites following this convention do not have any second FRAME or ANIMATION on ANGLE1 and ANGLE5.

See the revenant's first walking FRAME for example:

SKULA1

Mirrored frames

In addition to ANGLE1 and ANGLE2, FRAME1 and FRAME2 can also be different.

Pattern:

${PREFIX}${FRAME1}${ANGLE1}${FRAME2}${ANGLE2}

For example:

BOS2A3C7

In this case, the PREFIX of the animation is BOS2 (the Hell Knight). The name of the file tells us that this image is used for both FRAME A (first walk animation) of ANGLE 3 (left-facing) and FRAME C (third walk animation) of ANGLE 7 (right-facing).

Filenames which follow this convention are automatically mirrorred when displaying FRAME2 ANGLE2. In fact, the second half of the animation is a mirrored repeat of the first half.

Sprites following this convention end up with a front-facing and rear-facing angle that merely repeats the same frame for the second part of the animation. See the example of the Archvile:

VILEA5D5

Mix-and-match

Certain sprites use both the mirrored angle convention and the mirrored frames convention for the same FRAME.

Here is the first FRAME ANGLE of the walk animation of the Spider Mastermind:

SPIDA1D1

And here is the second ANGLE of the first FRANE of its walk animation:

SPIDA2A8

Filenames which follow this convention use both repeated frames for the second half of the animation on specific angles (1 and 5) as well as mirrored angle on the same FRAME