Added overworld battles

lib/BattleHud.lua

@@ -0,0 +1,349 @@
+-- Overworld battles: the HUD's footing on a world that is not white.
+--
+-- Gen 1 draws its battle HUDs as black glyphs and bar tiles straight onto
+-- the white field, with no box around them -- the field IS the backing. Take
+-- the field away and put a route underneath and the name, the level and the
+-- HP numbers are black on grass, which is not readable.
+--
+-- So each HUD block gets a panel: the world behind it, blurred to frosted
+-- glass and laid back down translucent, with a tint that pushes it away from
+-- whatever colour the text is about to be. Frosted rather than opaque
+-- because the point of the mode is that you can see where you are standing,
+-- and an opaque slab in the corner of the frame is the white field back
+-- again by another name.
+--
+-- And the text flips. A panel over a sunlit meadow is bright and wants black
+-- glyphs; the same panel over a cave floor or a dark roof is not, and wants
+-- white ones. So the panel's average brightness is measured and the glyphs
+-- follow it, with hysteresis so a slow camera drift across the threshold
+-- cannot strobe them.
+--
+-- The measurement is a one-pixel readback, which is a GPU stall, so it runs
+-- a few times a second rather than every frame. The camera drifts at about
+-- a pixel a second; brightness cannot outrun that.
+
+-- the mod namespace (see main.lua): V.require loads a sibling module
+local V = ...
+
+local BattleHud = {}
+
+-- How solid the frost is over the world behind it, and how far the tint
+-- pushes it toward the far end from the text.
+--
+-- Both deliberately light. The panel is there to make glyphs legible, not to
+-- put a slab in the corner of the frame: at these values the sharp world
+-- still reads through it and the blur registers as a pane of glass rather
+-- than as a second background.
+BattleHud.FROST = 0.55
+BattleHud.TINT = 0.26
+
+-- The luminance the glyphs flip at, with a dead band so a drift across it
+-- settles rather than strobes.
+BattleHud.DARK_ENTER = 0.44   -- below this, the panel is dark: white glyphs
+BattleHud.DARK_LEAVE = 0.56   -- above this, back to black ones
+
+-- Frames between brightness readbacks.
+BattleHud.SAMPLE_EVERY = 12
+
+-- The frost buffer's height; width follows the source's aspect. Small on
+-- purpose: the downscale is most of the blur, and what is read back for the
+-- brightness is one pixel of it.
+BattleHud.FROST_H = 72
+
+local frost, frostW, frostH = nil, 0, 0
+local blurA, blurB = nil, nil
+local probe = nil
+local frame = 0
+local luma = {}      -- panel key -> { value, dark, at }
+
+local SHADER = [[
+  uniform vec2 dir;
+  vec4 effect(vec4 color, Image tex, vec2 tc, vec2 sc) {
+    vec4 sum = Texel(tex, tc) * 0.2270270270;
+    sum += (Texel(tex, tc + dir) + Texel(tex, tc - dir)) * 0.1945945946;
+    sum += (Texel(tex, tc + 2.0 * dir) + Texel(tex, tc - 2.0 * dir)) * 0.1216216216;
+    sum += (Texel(tex, tc + 3.0 * dir) + Texel(tex, tc - 3.0 * dir)) * 0.0540540541;
+    sum += (Texel(tex, tc + 4.0 * dir) + Texel(tex, tc - 4.0 * dir)) * 0.0162162162;
+    return sum * color;
+  }
+]]
+
+local shader = nil            -- nil = untried, false = unavailable
+
+local function getShader()
+  if shader == nil then
+    local ok, sh = pcall(love.graphics.newShader, SHADER)
+    shader = (ok and sh) or false
+  end
+  return shader or nil
+end
+
+local function canvasOf(w, h, filter)
+  local ok, c = pcall(love.graphics.newCanvas, w, h)
+  if not ok then return nil end
+  c:setFilter(filter or "linear", filter or "linear")
+  return c
+end
+
+-- Build (or rebuild) the frosted copy of `src` for this frame.
+--
+-- Two steps, because one is not enough: the downscale to a 72-row buffer
+-- averages the world down to something that no longer reads as terrain, and
+-- the separable gaussian over that turns the remaining structure into
+-- frosted glass rather than a mosaic of the tiles it came from.
+function BattleHud.build(src)
+  if not src then return nil end
+  local blur = getShader()
+  local sw, sh = src:getDimensions()
+  if sw <= 0 or sh <= 0 then return nil end
+  local h = BattleHud.FROST_H
+  local w = math.max(1, math.floor(sw * h / sh + 0.5))
+  if not frost or frostW ~= w or frostH ~= h then
+    frost = canvasOf(w, h)
+    blurA = canvasOf(w, h)
+    blurB = canvasOf(w, h)
+    probe = probe or canvasOf(1, 1)
+    if not (frost and blurA and blurB) then
+      frost, blurA, blurB, frostW, frostH = nil, nil, nil, 0, 0
+      return nil
+    end
+    frostW, frostH = w, h
+  end
+
+  local prevCanvas = love.graphics.getCanvas()
+  local prevBlend, prevAlpha = love.graphics.getBlendMode()
+  local prevFilter = { src:getFilter() }
+  src:setFilter("linear", "linear")
+  love.graphics.setColor(1, 1, 1, 1)
+  love.graphics.setBlendMode("replace", "premultiplied")
+
+  local ok = pcall(function()
+    love.graphics.setCanvas(frost)
+    love.graphics.draw(src, 0, 0, 0, w / sw, h / sh)
+    if blur then
+      love.graphics.setShader(blur)
+      love.graphics.setCanvas(blurA)
+      pcall(blur.send, blur, "dir", { 2.5 / w, 0 })
+      love.graphics.draw(frost)
+      love.graphics.setCanvas(blurB)
+      pcall(blur.send, blur, "dir", { 0, 2.5 / h })
+      love.graphics.draw(blurA)
+      love.graphics.setShader()
+      frost, blurB = blurB, frost   -- the blurred one is the frost now
+    end
+  end)
+
+  love.graphics.setShader()
+  if prevCanvas then
+    love.graphics.setCanvas(prevCanvas)
+  else
+    love.graphics.setCanvas()
+  end
+  love.graphics.setBlendMode(prevBlend or "alpha", prevAlpha)
+  src:setFilter(prevFilter[1] or "nearest", prevFilter[2] or "nearest")
+  frame = frame + 1
+  return ok and frost or nil
+end
+
+function BattleHud.frame()
+  return frame
+end
+
+-- Average luminance of the frost under `key`'s rect, in frost-canvas pixels.
+--
+-- Averaged by letting the GPU do it: the rect is drawn into a one-pixel
+-- canvas, which IS the mean, and that one pixel is read back. Cached for
+-- SAMPLE_EVERY frames because the readback synchronises the pipeline and
+-- nothing it measures moves faster than that.
+local function sampleLuma(key, fx, fy, fw, fh)
+  local hit = luma[key]
+  if hit and (frame - hit.at) < BattleHud.SAMPLE_EVERY then return hit.value end
+  if not (frost and probe and frostW > 0) then return hit and hit.value end
+  if fw <= 0 or fh <= 0 then return hit and hit.value end
+
+  local prevCanvas = love.graphics.getCanvas()
+  local prevBlend, prevAlpha = love.graphics.getBlendMode()
+  local value = hit and hit.value or 1
+  local ok = pcall(function()
+    love.graphics.setCanvas(probe)
+    love.graphics.setBlendMode("replace", "premultiplied")
+    love.graphics.setColor(1, 1, 1, 1)
+    local quad = love.graphics.newQuad(fx, fy, fw, fh, frostW, frostH)
+    love.graphics.draw(frost, quad, 0, 0, 0, 1 / fw, 1 / fh)
+    love.graphics.setCanvas()
+    local data = probe:newImageData()
+    local r, g, b = data:getPixel(0, 0)
+    if data.release then pcall(data.release, data) end
+    value = 0.299 * r + 0.587 * g + 0.114 * b
+  end)
+
+  if prevCanvas then
+    love.graphics.setCanvas(prevCanvas)
+  else
+    love.graphics.setCanvas()
+  end
+  love.graphics.setBlendMode(prevBlend or "alpha", prevAlpha)
+  if not ok then return hit and hit.value end
+
+  luma[key] = { value = value, at = frame }
+  return value
+end
+
+-- Map a GB-frame rect onto the frost canvas, given where the letterbox sits
+-- in the source the frost was built from.
+local function frostRect(rect, box)
+  local kx = frostW / box.pw
+  local ky = frostH / box.ph
+  local fx = (box.lx + rect[1] * box.scale) * kx
+  local fy = (box.ly + rect[2] * box.scale) * ky
+  local fw = rect[3] * box.scale * kx
+  local fh = rect[4] * box.scale * ky
+  return fx, fy, math.max(1, fw), math.max(1, fh)
+end
+
+-- ------- the verdict
+--
+-- ONE answer for the whole frame, not one per panel. Both HUDs draw in a
+-- single pass and there is only one glyph colour to be had out of it -- and
+-- a frame with a black-lettered HUD in one corner and a white-lettered one
+-- in the other would read as a bug rather than as adaptation. The DARKER
+-- panel decides, because it is the one that cannot afford to be wrong, and
+-- the tint below then commits both panels to that reading.
+local wasDark = false
+
+function BattleHud.verdict(rects, box)
+  if not (frost and box and box.scale and box.scale > 0) then return false end
+  local darkest = nil
+  for key, rect in pairs(rects) do
+    local fx, fy, fw, fh = frostRect(rect, box)
+    local v = sampleLuma(key, fx, fy, fw, fh)
+    if v and (not darkest or v < darkest) then darkest = v end
+  end
+  if not darkest then return wasDark end
+  -- hysteresis: it takes a clear move past the far threshold to flip back,
+  -- so a camera drifting across the boundary settles instead of strobing
+  if wasDark then
+    wasDark = darkest < BattleHud.DARK_LEAVE
+  else
+    wasDark = darkest < BattleHud.DARK_ENTER
+  end
+  return wasDark
+end
+
+-- Draw one HUD panel into the current target, in GB coordinates.
+--
+-- The tint always pushes AWAY from the glyph colour that is about to be
+-- used, so the contrast is guaranteed rather than hoped for: a dark panel
+-- gets darker under white text, a bright one brighter under black text.
+function BattleHud.panel(rect, box, dark)
+  if not (frost and box and box.scale and box.scale > 0) then return false end
+  local fx, fy, fw, fh = frostRect(rect, box)
+  local ok = pcall(function()
+    local quad = love.graphics.newQuad(fx, fy, fw, fh, frostW, frostH)
+    love.graphics.setColor(1, 1, 1, BattleHud.FROST)
+    love.graphics.draw(frost, quad, rect[1], rect[2], 0,
+                       rect[3] / fw, rect[4] / fh)
+    local shade = dark and 0 or 1
+    love.graphics.setColor(shade, shade, shade, BattleHud.TINT)
+    love.graphics.rectangle("fill", rect[1], rect[2], rect[3], rect[4])
+    love.graphics.setColor(1, 1, 1, 1)
+  end)
+  return ok
+end
+
+-- ------- flipping the glyphs
+--
+-- Over a dark panel the HUD's black text has to go white, and it cannot be
+-- done by setting a draw colour: LOVE MULTIPLIES by it, and a black glyph
+-- times white is still black. The colour channel has to be REPLACED.
+--
+-- So the HUD is drawn into a scratch layer and that layer is composited back
+-- through a shader that whitens whatever is nearly black and leaves the rest
+-- alone. "Nearly black" is the text, the tick marks and the bar's outline --
+-- everything the HUD draws as ink -- while the HP bar's own greens and reds
+-- are well clear of the threshold and come through untouched.
+--
+-- Composited back into whatever the caller had bound, which is what makes it
+-- work in both pipelines without knowing which one it is in: in the colorized
+-- one that target is the grayscale BG canvas, where white IS shade 0 and the
+-- zone pass then colours the flipped glyphs like every other lightest-shade
+-- surface; in the flat fallback it is the screen, where white is white.
+local INK = 0.35   -- luminance at or under which a pixel counts as ink
+
+local FLIP = [[
+  uniform float ink;
+  vec4 effect(vec4 color, Image tex, vec2 tc, vec2 sc) {
+    vec4 p = Texel(tex, tc);
+    float luma = dot(p.rgb, vec3(0.299, 0.587, 0.114));
+    if (p.a > 0.0 && luma <= ink * p.a) p.rgb = vec3(p.a);
+    return p * color;
+  }
+]]
+
+local flipShader = nil
+local layer = nil
+
+local function getFlip()
+  if flipShader == nil then
+    local ok, sh = pcall(love.graphics.newShader, FLIP)
+    flipShader = (ok and sh) or false
+  end
+  return flipShader or nil
+end
+
+-- Whether the flip pass can run at all, for the shot driver's log.
+function BattleHud.flipReady()
+  return getFlip() ~= nil
+end
+
+-- Run `fn` with its ink whitened. Falls back to running it plainly when the
+-- scratch layer or the shader is unavailable, so a driver that cannot do
+-- either gets the vanilla black HUD rather than no HUD.
+function BattleHud.flipGlyphs(w, h, fn)
+  local sh = getFlip()
+  if not sh then return fn() end
+  if not layer or layer:getWidth() ~= w or layer:getHeight() ~= h then
+    layer = canvasOf(w, h, "nearest")
+    if not layer then return fn() end
+  end
+
+  local prevCanvas = love.graphics.getCanvas()
+  local prevBlend, prevAlpha = love.graphics.getBlendMode()
+  local ok, err = pcall(function()
+    love.graphics.setCanvas(layer)
+    love.graphics.clear(0, 0, 0, 0)
+    love.graphics.setBlendMode("alpha")
+    fn()
+  end)
+  if prevCanvas then
+    love.graphics.setCanvas(prevCanvas)
+  else
+    love.graphics.setCanvas()
+  end
+  love.graphics.setBlendMode(prevBlend or "alpha", prevAlpha)
+  if not ok then error(err, 0) end
+
+  love.graphics.setShader(sh)
+  pcall(sh.send, sh, "ink", INK)
+  love.graphics.setColor(1, 1, 1, 1)
+  love.graphics.draw(layer, 0, 0)
+  love.graphics.setShader()
+end
+
+-- The last luminance measured, for the shot driver's log.
+function BattleHud.lastLuma()
+  local best = nil
+  for _, hit in pairs(luma) do
+    if not best or hit.value < best then best = hit.value end
+  end
+  return best
+end
+
+function BattleHud.invalidate()
+  frost, blurA, blurB, probe = nil, nil, nil, nil
+  frostW, frostH = 0, 0
+  luma = {}
+  wasDark = false
+end
+
+return BattleHud