From ddff583784c4f11a12e1a41086d4136d1432186f Mon Sep 17 00:00:00 2001
From: Michele Tampellini <mic.tampellini@gmail.com>
Date: Mon, 6 Dec 2021 11:59:56 +0700
Subject: [PATCH] Letterboxing window flag

---
 src/raylib.h |  1 +
 src/rcore.c  | 30 +++++++++++++++++++++++-------
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/raylib.h b/src/raylib.h
index 41d23bfad..734c28269 100644
--- a/src/raylib.h
+++ b/src/raylib.h
@@ -497,6 +497,7 @@ typedef enum {
     FLAG_WINDOW_ALWAYS_RUN  = 0x00000100,   // Set to allow windows running while minimized
     FLAG_WINDOW_TRANSPARENT = 0x00000010,   // Set to allow transparent framebuffer
     FLAG_WINDOW_HIGHDPI     = 0x00002000,   // Set to support HighDPI
+    FLAG_FIXED_RENDER_SIZE  = 0x00004000,   // Set to lock the render size (aka letterbox-resize the whole window)
     FLAG_MSAA_4X_HINT       = 0x00000020,   // Set to try enabling MSAA 4X
     FLAG_INTERLACED_HINT    = 0x00010000    // Set to try enabling interlaced video format (for V3D)
 } ConfigFlags;
diff --git a/src/rcore.c b/src/rcore.c
index 946ed0c0c..2e0895cb2 100644
--- a/src/rcore.c
+++ b/src/rcore.c
@@ -2200,14 +2200,21 @@ void BeginScissorMode(int x, int y, int width, int height)
     Vector2 scale = GetWindowScaleDPI();
     rlScissor((int)(x*scale.x), (int)(GetScreenHeight()*scale.y - (((y + height)*scale.y))), (int)(width*scale.x), (int)(height*scale.y));
 #else
+    Vector2 scale = { 1, 1 };
     if ((CORE.Window.flags & FLAG_WINDOW_HIGHDPI) > 0)
     {
         Vector2 scale = GetWindowScaleDPI();
-        rlScissor((int)(x*scale.x), (int)(CORE.Window.currentFbo.height - (y + height)*scale.y), (int)(width*scale.x), (int)(height*scale.y));
+    }
+
+    if (CORE.Window.flags & FLAG_FIXED_RENDER_SIZE)
+    {
+        float rapw = ((float)CORE.Window.render.width / (float)CORE.Window.currentFbo.width);
+        float raph = ((float)CORE.Window.render.height / (float)CORE.Window.currentFbo.height);
+        rlScissor(((float)x / rapw)*scale.x, (float)CORE.Window.currentFbo.height - ((((float)y / raph) + ((float)height / raph))*scale.y), ((float)width / rapw)*scale.x, ((float)height / raph)*scale.y);
     }
     else
     {
-        rlScissor(x, CORE.Window.currentFbo.height - (y + height), width, height);
+        rlScissor((int)(x*scale.x), (int)(CORE.Window.currentFbo.height - (y + height)*scale.y), (int)(width*scale.x), (int)(height*scale.y));
     }
 #endif
 }
@@ -3574,7 +3581,11 @@ Vector2 GetMousePosition(void)
     position.x = (CORE.Input.Mouse.currentPosition.x + CORE.Input.Mouse.offset.x)*CORE.Input.Mouse.scale.x;
     position.y = (CORE.Input.Mouse.currentPosition.y + CORE.Input.Mouse.offset.y)*CORE.Input.Mouse.scale.y;
 #endif
-
+    if (CORE.Window.flags & FLAG_FIXED_RENDER_SIZE)
+    {
+        position.x *= ((float)CORE.Window.render.width / (float)CORE.Window.currentFbo.width);
+        position.y *= ((float)CORE.Window.render.height / (float)CORE.Window.currentFbo.height);
+    }
     return position;
 }
 
@@ -4476,9 +4487,6 @@ static bool InitGraphicsDevice(int width, int height)
 // Set viewport for a provided width and height
 static void SetupViewport(int width, int height)
 {
-    CORE.Window.render.width = width;
-    CORE.Window.render.height = height;
-
     // Set viewport width and height
     // NOTE: We consider render size (scaled) and offset in case black bars are required and
     // render area does not match full display area (this situation is only applicable on fullscreen mode)
@@ -4487,7 +4495,15 @@ static void SetupViewport(int width, int height)
     glfwGetWindowContentScale(CORE.Window.handle, &xScale, &yScale);
     rlViewport(CORE.Window.renderOffset.x/2*xScale, CORE.Window.renderOffset.y/2*yScale, (CORE.Window.render.width)*xScale, (CORE.Window.render.height)*yScale);
 #else
-    rlViewport(CORE.Window.renderOffset.x/2, CORE.Window.renderOffset.y/2, CORE.Window.render.width, CORE.Window.render.height);
+    if (!(CORE.Window.flags & FLAG_FIXED_RENDER_SIZE))
+    {
+        CORE.Window.render.width = width;
+        CORE.Window.render.height = height;
+        rlViewport(CORE.Window.renderOffset.x / 2, CORE.Window.renderOffset.y / 2, CORE.Window.render.width - CORE.Window.renderOffset.x, CORE.Window.render.height - CORE.Window.renderOffset.y);
+    }
+    else
+        rlViewport(CORE.Window.renderOffset.x / 2, CORE.Window.renderOffset.y / 2, width - CORE.Window.renderOffset.x, height - CORE.Window.renderOffset.y);
+
 #endif
 
     rlMatrixMode(RL_PROJECTION);        // Switch to projection matrix