From e381c75d8c1b76afecb9eb7e9f91884fa2a44dd8 Mon Sep 17 00:00:00 2001
From: Guido Cella <guido@guidocella.xyz>
Date: Sat, 12 Feb 2022 11:53:50 +0100
Subject: [PATCH] add cursor-centric-zoom

---
 input.conf                    |  4 ++--
 scripts/image-keybindings.lua | 27 +++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/input.conf b/input.conf
index 55538d6..bbd84de 100644
--- a/input.conf
+++ b/input.conf
@@ -78,5 +78,5 @@ MBTN_LEFT  {image} script-binding gesture
 MBTN_LEFT_DBL {image} ignore
 MBTN_MID   {image} script-binding align-to-cursor
 MBTN_RIGHT {image} script-binding drag-to-pan
-WHEEL_UP   {image} no-osd add video-zoom .1
-WHEEL_DOWN {image} no-osd add video-zoom -.1
+WHEEL_UP   {image} script-message cursor-centric-zoom .1
+WHEEL_DOWN {image} script-message cursor-centric-zoom -.1
diff --git a/scripts/image-keybindings.lua b/scripts/image-keybindings.lua
index 9ba5be2..b7b0620 100644
--- a/scripts/image-keybindings.lua
+++ b/scripts/image-keybindings.lua
@@ -90,6 +90,33 @@ mp.add_key_binding(nil, 'drag-to-pan', function (table)
     end)
 end, { complex = true })
 
+mp.register_script_message('cursor-centric-zoom', function (amount)
+    local mouse_pos = mp.get_property_native('mouse-pos')
+    local dims = mp.get_property_native('osd-dimensions')
+    local width = (dims.w - dims.ml - dims.mr) * 2^amount
+    local height = (dims.h - dims.mt - dims.mb) * 2^amount
+    local command = 'no-osd add video-zoom ' .. amount .. ';'
+
+    if width > dims.w then
+        local old_cursor_ml = dims.ml - mouse_pos.x
+        local cursor_ml = old_cursor_ml * 2^amount
+        local ml = cursor_ml + mouse_pos.x
+        -- from video/out/aspect.c:src_dst_split_scaling() we know that:
+        -- ml = (osd-width - width) * (video-align-x + 1) / 2
+        -- so video-align-x is:
+        local video_align_x = 2 * ml / (dims.w - width) - 1
+        command = command .. 'no-osd set video-align-x ' .. math.min(1, math.max(video_align_x, -1)) .. ';'
+    end
+
+    if height > dims.h then
+        local mt = (dims.mt - mouse_pos.y) * 2^amount + mouse_pos.y
+        local video_align_y = 2 * mt / (dims.h - height) - 1
+        command = command .. 'no-osd set video-align-y ' .. math.min(1, math.max(video_align_y, -1))
+    end
+
+    mp.command(command)
+end)
+
 local is_intial_callback
 local function undo_lavfi_complex()
     if is_intial_callback then
-- 
2.45.2