#!/usr/bin/env bash
# ─────────────────────────────────────────────────────────────────────
# mimecroft-frag.sh — MIMEcroft's fragment shader, AUTHORED IN BASH and
# compiled to GLSL by the sh→GLSL backend (glsl_backend.rs in the
# sh2perl repo; `sh2glsl` command). The game writes this program to
# /tmp at startup (emit_fragment_shader) and compiles it; the generated
# GLSL ES 1.00 fragment shader is loaded into /dev/webgl/shader/fragment.
# __shader-test.mjs assembles the game's INLINE program from
# emit_fragment_shader and asserts it equals this file's code section.
#
# Inputs (bridged by the generator, all ints):
#   frag_x, frag_y   ← int(gl_FragCoord.xy)
#   vcolor_r/g/b     ← int(vColor.rgb * 127.0)   (the vertex shader's
#                      varying — the block colour, 0..127 scale)
#   tex_r/g/b        ← the sampled block-texture texel (0-255)
#   damage, cr_r/g/a ← the crack-overlay level + texel (0..127 scale)
# Output: out_buf bytes 0..3 = R, G, B, A  (via `putb N`)
#
# MEDIUMP-INT DISCIPLINE (ES 1.00 mandatory precision — ±2^15): every
# product is bounded before its division, so no intermediate exceeds
# 32767 and the backend can emit `precision mediump int;`:
#   tint  r·tex_r/128:  r ≤ 127, tex_r ≤ 255  → 32385
#   CRT   r·90/100:  r ≤ 254  → 22860   (runs BEFORE the blend)
#   blend (r-cr_r)·mix/128:  |r-cr_r| ≤ 228, mix ≤ 127  → 28956
#   (mix = damage·cr_a caps at 127 on the FIRST hit, so the crack texel
#   takes ~99% of the blend at ANY damage level — the dark GRAY crack
#   colour dominates from the first shot and the block's own hue never
#   tints the crack lines; the crack appears fully at damage 1 and the
#   block breaks at its hardness)
#   vig   r·dim/256:  r ≤ 342, dim ≤ 30  → 10260
# 127/128 ≈ 255/255 keeps the output range (tint max 253 ≈ 255), so
# the 0..127 colour scale is visually identical to the old 0..255.
#
# Effects (pure integer arithmetic — GLSL has no strings, the backend
# has no floats):
#   • block texture × colour tint
#   • damage: mix in the crack texture by the damage level
#   • CRT scanline:  every 6th row dims 10%
#   • corruption:    a deterministic hash of the pixel position throws
#                    1 in 97 pixels into red (the evil-MIME glare)
#   • vignette:      corners darken toward the 800×600 frame edge
#
# fx/fy (the gl_FragCoord bridge) are used ONLY by those effects — the
# game emits them conditionally (emit_fragment_shader adds them only
# when CRT or corruption is enabled), so the no-effects shader has no
# per-fragment gl_FragCoord reads. This file is the FULL program (all
# effects on) — the canonical reference for the shader gate.
# ─────────────────────────────────────────────────────────────────────
fx=$((frag_x))
fy=$((frag_y))
r=$((vcolor_r))
g=$((vcolor_g))
b=$((vcolor_b))
r=$((r * tex_r / 128))
g=$((g * tex_g / 128))
b=$((b * tex_b / 128))
scan=$((fy % 6))
if [ "$scan" -eq 0 ]; then
  r=$((r * 90 / 100))
  g=$((g * 90 / 100))
  b=$((b * 90 / 100))
fi
if [ "$damage" -gt 0 ]; then
  mix=$((damage * cr_a))
  if [ "$mix" -gt 127 ]; then mix=127; fi
  r=$((r - (r - cr_r) * mix / 128))
  g=$((g - (g - cr_g) * mix / 128))
  b=$((b - (b - cr_b) * mix / 128))
fi
hash=$((fx * 7 + fy * 13))
corrupt=$((hash % 97))
if [ "$corrupt" -eq 0 ]; then
  r=255
  g=$((g / 2))
  b=$((b / 2))
fi
vx=$((fx - 400))
vy=$((fy - 300))
if [ "$vx" -lt 0 ]; then vx=$((0 - vx)); fi
if [ "$vy" -lt 0 ]; then vy=$((0 - vy)); fi
edge=$((vx + vy))
if [ "$edge" -gt 450 ]; then
  dim=$((edge - 450))
  if [ "$dim" -gt 30 ]; then dim=30; fi
  r=$((r - r * dim / 256))
  g=$((g - g * dim / 256))
  b=$((b - b * dim / 256))
fi
if [ "$r" -lt 0 ]; then r=0; fi
if [ "$g" -lt 0 ]; then g=0; fi
if [ "$b" -lt 0 ]; then b=0; fi
putb $r
putb $g
putb $b
putb 255