From af6e0224545528bd31fda371c7f1d0e1a2b73e63 Mon Sep 17 00:00:00 2001
From: Lucas Scharenbroich <lscharen@prowestgis.com>
Date: Thu, 23 Feb 2023 19:24:09 -0600
Subject: [PATCH] WIP for working through scanline algos

---
 tools/scanline-test.py | 105 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)
 create mode 100644 tools/scanline-test.py

diff --git a/tools/scanline-test.py b/tools/scanline-test.py
new file mode 100644
index 0000000..396e06e
--- /dev/null
+++ b/tools/scanline-test.py
@@ -0,0 +1,105 @@
+# Playground for working through scanline decomposition algorithm
+
+# 1. Shadow Off
+# 2. Draw Playfield (sprite OR overlay) AND NOT solid_overlay
+# 3. Draw sprites
+
+sprites = [
+    { 'top': 10, 'bottom': 17 },
+    { 'top': 14, 'bottom': 29 }
+]
+
+overlays = [
+    { 'top': 0, 'bottom': 7 }
+]
+
+MAX_HEIGHT = 199
+
+# Combine a list on ranges into a minimal list by merging overlapping ranges
+def simplify(a):
+    b = []
+    if len(a) > 0:
+        last = a[0]
+        start = last['top']
+        for r in a[1:]:
+            if r['top'] <= last['bottom']:
+                last = r
+                continue
+
+            b.append([start, last['bottom']])
+            last = r
+            start = r['top']
+        
+        b.append([start, last['bottom']])
+
+    return b
+
+# Given two sorted lists, merge them together into a minimal set of ranges.  This could
+# be done as a list merge nd then a combine step, but we want to be more efficient and
+# do the merge-and-compbine at the same time
+def merge(a, b):
+    if len(a) == 0:
+        return simplify(b)
+    
+    if len(b) == 0:
+        return simplify(a)
+
+    c = []
+    i = j = 0
+
+    while i < len(a) and j < len(b):
+        if a[i]['top'] <= b[j]['top']:
+            c.append(a[i])
+            i += 1
+        else:
+            c.append(b[j])
+            j += 1
+
+    if i < len(a):
+        c.extend(a[i:])
+
+    if j < len(b):
+        c.extend(b[j:])
+
+    return simplify(c)
+
+# Find the lines that need to be drawn with shadowing off
+def get_shadow_off_bg(sprites):
+    ranges = []
+
+    if len(sprites) > 0:
+        last = sprites[0]
+        start = last['top']
+
+        for sprite in sprites[1:]:
+            if sprite['top'] <= last['bottom']:
+                last = sprite
+                continue
+
+            ranges.push([start, last['bottom']])
+            start = sprite['top']
+            last = sprite
+        
+        ranges.append([start, last['bottom']])
+
+    return ranges
+
+def complement(ranges):
+    comp = []
+    if len(ranges) > 0:
+        if ranges[0][0] > 0:
+            comp.append([0, ranges[0][0]])
+        for i in range(1, len(ranges)):
+            comp.append([ranges[i-1][1]+1, ranges[i][0]])
+        last = ranges[len(ranges)-1]
+        if last[1] < MAX_HEIGHT:
+            comp.append([last[1]+1, MAX_HEIGHT])
+        return comp
+    else:
+        return [0, MAX_HEIGHT]
+
+r = get_shadow_off_bg(sprites)
+print(r)
+print(complement(r))
+
+print(merge(sprites, overlays))
\ No newline at end of file