From 26ff5e112626399e388a93bdb80f731d1cd7fe7f Mon Sep 17 00:00:00 2001
From: Fabian Greffrath <fabian@greffrath.com>
Date: Wed, 13 Mar 2024 17:14:36 +0100
Subject: [PATCH] additional screen wipe: fizzle fade from Wolf 3D (#1586)

* alternative screen wipe: fizzle fade from Wolf 3D

* comment out static functions to let CI pass

* copy one "pixel" at a time

* add as a third alternative
---
 src/f_wipe.c   | 124 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/f_wipe.h   |   1 +
 src/m_config.c |   4 +-
 src/mn_setup.c |   2 +-
 4 files changed, 128 insertions(+), 3 deletions(-)

diff --git a/src/f_wipe.c b/src/f_wipe.c
index dfbaca22..0f4d2115 100644
--- a/src/f_wipe.c
+++ b/src/f_wipe.c
@@ -214,6 +214,127 @@ static int wipe_NOP(int x, int y, int t)
   return 0;
 }
 
+/*
+// Copyright(C) 1992 Id Software, Inc.
+// Copyright(C) 2007-2011 Moritz "Ripper" Kroll
+
+===================
+=
+= FizzleFade
+=
+= It uses maximum-length Linear Feedback Shift Registers (LFSR) counters.
+= You can find a list of them with lengths from 3 to 168 at:
+= http://www.xilinx.com/support/documentation/application_notes/xapp052.pdf
+= Many thanks to Xilinx for this list!!!
+=
+===================
+*/
+
+// XOR masks for the pseudo-random number sequence starting with n=17 bits
+static const uint32_t rndmasks[] = {
+                    // n    XNOR from (starting at 1, not 0 as usual)
+    0x00012000,     // 17   17,14
+    0x00020400,     // 18   18,11
+    0x00040023,     // 19   19,6,2,1
+    0x00090000,     // 20   20,17
+    0x00140000,     // 21   21,19
+    0x00300000,     // 22   22,21
+    0x00420000,     // 23   23,18
+    0x00e10000,     // 24   24,23,22,17
+    0x01200000,     // 25   25,22      (this is enough for 8191x4095)
+};
+
+// Returns the number of bits needed to represent the given value
+static int log2_ceil(uint32_t x)
+{
+    int n = 0;
+    uint32_t v = 1;
+
+    while (v < x)
+    {
+        n++;
+        v <<= 1;
+    }
+
+    return n;
+}
+
+static unsigned int rndbits_y;
+static unsigned int rndmask;
+static unsigned int lastrndval;
+
+static int wipe_initFizzle(int width, int height, int ticks)
+{
+    int rndbits_x = log2_ceil(video.unscaledw);
+    rndbits_y = log2_ceil(COLUMN_MAX_Y);
+
+    int rndbits = rndbits_x + rndbits_y;
+    if (rndbits < 17)
+        rndbits = 17; // no problem, just a bit slower
+    else if (rndbits > 25)
+        rndbits = 25; // fizzle fade will not fill whole screen
+
+    rndmask = rndmasks[rndbits - 17];
+
+    V_PutBlock(0, 0, width, height, wipe_scr_start);
+
+    lastrndval = 0;
+
+    return 0;
+}
+
+static int wipe_doFizzle(int width, int height, int ticks)
+{
+    const int pixperframe = (video.unscaledw * COLUMN_MAX_Y) >> 5;
+    unsigned int rndval = lastrndval;
+
+    for (unsigned p = 0; p < pixperframe; p++)
+    {
+        // seperate random value into x/y pair
+
+        unsigned int x = rndval >> rndbits_y;
+        unsigned int y = rndval & ((1 << rndbits_y) - 1);
+
+        // advance to next random element
+
+        rndval = (rndval >> 1) ^ (rndval & 1 ? 0 : rndmask);
+
+        if (x >= video.unscaledw || y >= COLUMN_MAX_Y)
+        {
+            if (rndval == 0) // entire sequence has been completed
+            {
+                return true;
+            }
+
+            p--;
+            continue;
+        }
+
+        // copy one pixel
+        vrect_t rect = {x, y, 1, 1};
+        V_ScaleRect(&rect);
+
+        byte *src = wipe_scr_end + rect.sy * width + rect.sx;
+        byte *dest = wipe_scr + rect.sy * video.pitch + rect.sx;
+
+        while (rect.sh--)
+        {
+            memcpy(dest, src, rect.sw);
+            src += width;
+            dest += video.pitch;
+        }
+
+        if (rndval == 0) // entire sequence has been completed
+        {
+            return true;
+        }
+    }
+
+    lastrndval = rndval;
+
+    return false;
+}
+
 static int (*const wipes[])(int, int, int) = {
   wipe_NOP,
   wipe_NOP,
@@ -224,6 +345,9 @@ static int (*const wipes[])(int, int, int) = {
   wipe_initColorXForm,
   wipe_doColorXForm,
   wipe_exit,
+  wipe_initFizzle,
+  wipe_doFizzle,
+  wipe_exit,
 };
 
 // killough 3/5/98: reformatted and cleaned up
diff --git a/src/f_wipe.h b/src/f_wipe.h
index 1121bf9f..28e760c3 100644
--- a/src/f_wipe.h
+++ b/src/f_wipe.h
@@ -28,6 +28,7 @@ enum {
   wipe_None,
   wipe_Melt,        // weird screen melt
   wipe_ColorXForm,
+  wipe_Fizzle,
   wipe_NUMWIPES
 };
 
diff --git a/src/m_config.c b/src/m_config.c
index 5b6410bd..84d9592d 100644
--- a/src/m_config.c
+++ b/src/m_config.c
@@ -606,8 +606,8 @@ default_t defaults[] = {
   {
     "screen_melt",
     (config_t *) &screen_melt, NULL,
-    {wipe_Melt}, {wipe_None, wipe_ColorXForm}, number, ss_gen, wad_no,
-    "screen wipe effect (0 = none, 1 = melt, 2 = crossfade)"
+    {wipe_Melt}, {wipe_None, wipe_Fizzle}, number, ss_gen, wad_no,
+    "screen wipe effect (0 = none, 1 = melt, 2 = crossfade, 3 = fizzlefade)"
   },
 
   {
diff --git a/src/mn_setup.c b/src/mn_setup.c
index dbe8c12d..6dac8b1a 100644
--- a/src/mn_setup.c
+++ b/src/mn_setup.c
@@ -2253,7 +2253,7 @@ const char *default_skill_strings[] = {
 static const char *death_use_action_strings[] = {"default", "last save",
                                                  "nothing"};
 
-static const char *screen_melt_strings[] = {"Off", "Melt", "Crossfade"};
+static const char *screen_melt_strings[] = {"Off", "Melt", "Crossfade", "Fizzle"};
 
 static const char *invul_mode_strings[] = {"Vanilla", "MBF", "Gray"};