72 lines
3.1 KiB
Text
72 lines
3.1 KiB
Text
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shader_type canvas_item;
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// #125: the dimensional breach, as a screen-space lens.
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//
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// The prologue's warp used to be a handful of lines turning around a point.
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// This bends the ACTUAL SCENE around the breach instead - the ships, the
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// rocks and the starfield all get dragged into it - which is most of what
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// makes a hole in space read as a hole rather than as a decal drawn on top
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// of one.
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//
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// Two effects, both radial and both fading to nothing at the edge of their
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// reach, so the shader is invisible outside its own radius and costs a
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// clamped texture fetch everywhere else:
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//
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// swirl angle offset that grows toward the centre, so the scene winds
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// around the hole rather than merely sliding toward it
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// pull inward displacement, strongest just outside the horizon, which
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// is the lensing itself
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//
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// Inside the horizon nothing is sampled at all: the core is drawn as empty,
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// the same decision BlackHoleVisual makes for the black-hole planet, and
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// for the same reason - a "black hole" with something visible in the middle
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// stops reading as one.
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uniform sampler2D screen_texture : hint_screen_texture, repeat_disable, filter_linear;
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// Where the breach is, in SCREEN pixels, and how big it has grown.
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uniform vec2 breach_center = vec2(360.0, 640.0);
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uniform vec2 viewport_size = vec2(720.0, 1280.0);
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// The event horizon: everything inside is void.
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uniform float horizon_radius = 0.0;
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// How far the lens reaches past the horizon. Beyond this the scene is
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// untouched.
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uniform float lens_radius = 1.0;
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// 0 while the breach is opening, 1 at full strength. Scales both effects
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// together so one knob fades the whole thing in.
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uniform float strength = 0.0;
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uniform float swirl_turns = 2.4;
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uniform vec4 rim_color : source_color = vec4(0.72, 0.45, 1.0, 1.0);
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void fragment() {
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vec2 pixel = UV * viewport_size;
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vec2 offset = pixel - breach_center;
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float distance_to_centre = length(offset);
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if (distance_to_centre >= lens_radius || strength <= 0.001) {
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COLOR = texture(screen_texture, SCREEN_UV);
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} else if (distance_to_centre <= horizon_radius) {
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// The core. Not black-with-alpha: genuinely nothing, so whatever is
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// behind the breach is gone rather than dimmed.
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COLOR = vec4(0.0, 0.0, 0.0, 1.0);
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} else {
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// 1 at the horizon, 0 at the edge of the lens. Squared so the bend
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// is concentrated near the hole instead of smeared evenly outward.
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float falloff = 1.0 - clamp(
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(distance_to_centre - horizon_radius) / max(lens_radius - horizon_radius, 1.0),
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0.0, 1.0);
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float bend = falloff * falloff * strength;
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float angle = atan(offset.y, offset.x) + bend * swirl_turns;
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float pulled = distance_to_centre - bend * (lens_radius - horizon_radius) * 0.55;
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pulled = max(pulled, horizon_radius);
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vec2 sampled = breach_center + vec2(cos(angle), sin(angle)) * pulled;
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COLOR = texture(screen_texture, sampled / viewport_size);
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// A hot rim where the lensing is fiercest, which is what gives the
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// horizon an edge rather than a fade.
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float rim = smoothstep(0.72, 1.0, falloff) * strength;
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COLOR.rgb = mix(COLOR.rgb, rim_color.rgb, rim * 0.65);
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}
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}
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