Add rainbow explosion

Credit to @PlayWithFurcifer for the [sprite sheet][1] and [tutorial][2]
that formed the basis of this explosion

I've made minor tweaks compared to the settings they used in the
tutorial, and had to work out how to translate the settings from the
Godot 3 `Particles2D` node to the Godot 4 `CPUParticles2D` node. Working
our how to add the texture was the trickiest part, but part of the
problem there was working out that it wanted an SVG, not a PNG. I
believe the Godot 3 `Particles2D` node is more equivalent to the Godot 4
`GPUParticles2D`, but [Godot crashes when trying to use this on a
project using the compatibility renderer on macOS][3]

[1]: https://github.com/PlayWithFurcifer/godot-particle-systems-guide/blob/main/Explosion_Sheet.png
[2]: https://www.youtube.com/watch?v=F1Fyj3Lh_Pc&t=253s
[3]: godotengine/godot#72469

README.md

@@ -5,6 +5,10 @@ Making a game for The Queerness and Games Jam 2023
 ## Credits
 
 [Flag sprites][flag-sprites] by [Rob Mocci][rob-mocci]
+[Explosion sprite sheet][explosion-sprite-sheet] and [guide][explosion-tutorial] by [PlayWithFurcifer][play-with-furcifer]
 
+[explosion-sprite-sheet]: https://github.com/PlayWithFurcifer/godot-particle-systems-guide/blob/main/Explosion_Sheet.png
+[explosion-tutorial]: https://www.youtube.com/watch?v=F1Fyj3Lh_Pc&t=253s
 [flag-sprites]: https://rmocci.itch.io/pixel-special
+[play-with-furcifer]: https://github.com/PlayWithFurcifer
 [rob-mocci]: https://rmocci.itch.io

assets/images/sprites/explosion_sheet.svg.import

@@ -0,0 +1,37 @@
+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://bc1djcrvyx3dk"
+path="res://.godot/imported/explosion_sheet.svg-9bb92ba2f81415d87d1ef9bc9b9091f6.ctex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://assets/images/sprites/explosion_sheet.svg"
+dest_files=["res://.godot/imported/explosion_sheet.svg-9bb92ba2f81415d87d1ef9bc9b9091f6.ctex"]
+
+[params]
+
+compress/mode=0
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=false
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=1
+svg/scale=1.0
+editor/scale_with_editor_scale=false
+editor/convert_colors_with_editor_theme=false

scenes/explosion.tscn

@@ -0,0 +1,34 @@
+[gd_scene load_steps=4 format=3 uid="uid://n3fd71xert8q"]
+
+[ext_resource type="Texture2D" uid="uid://bc1djcrvyx3dk" path="res://assets/images/sprites/explosion_sheet.svg" id="1_or2ic"]
+
+[sub_resource type="CanvasItemMaterial" id="CanvasItemMaterial_0noh1"]
+particles_animation = true
+particles_anim_h_frames = 5
+particles_anim_v_frames = 1
+particles_anim_loop = false
+
+[sub_resource type="Gradient" id="Gradient_xr1od"]
+interpolation_mode = 1
+offsets = PackedFloat32Array(0, 0.0822086, 0.165563, 0.252761, 0.334969, 0.415951, 0.492025, 0.581595, 0.665031, 0.749693, 0.83681, 0.920245, 1)
+colors = PackedColorArray(1, 1, 1, 1, 0.937255, 0.607843, 0.737255, 1, 0.847059, 0, 0.0745098, 1, 0.505882, 0.262745, 0.0705882, 1, 0.92549, 0.458824, 0.0784314, 1, 0.988235, 0.823529, 0.0823529, 1, 0.921569, 0.890196, 0.113725, 1, 0.403922, 0.682353, 0.12549, 1, 0.419608, 0.756863, 0.87451, 1, 0.133333, 0.262745, 0.576471, 1, 0.321569, 0.12549, 0.470588, 1, 0.34902, 0.0666667, 0.427451, 1, 0.0862745, 0.0862745, 0.0823529, 1)
+
+[node name="CPUParticles2D" type="CPUParticles2D"]
+material = SubResource("CanvasItemMaterial_0noh1")
+lifetime = 0.5
+one_shot = true
+speed_scale = 0.5
+explosiveness = 1.0
+lifetime_randomness = 0.5
+texture = ExtResource("1_or2ic")
+emission_shape = 1
+emission_sphere_radius = 128.0
+gravity = Vector2(2.08165e-12, -50)
+angular_velocity_max = 5.0
+angle_min = -720.0
+angle_max = 720.0
+scale_amount_min = 3.0
+scale_amount_max = 5.0
+color_ramp = SubResource("Gradient_xr1od")
+anim_speed_min = 1.0
+anim_speed_max = 1.0