From 2e93a75bb7fb4ec14928d3abc87c87ecb7edad7c Mon Sep 17 00:00:00 2001
From: Joris Bontje <jorisbontje@gmail.com>
Date: Wed, 21 Apr 2021 15:26:09 +0200
Subject: [PATCH] Add SVG scale transform and non-zero / negative viewbox
 offset

---
 examples/data/scale.svg       | 16 ++++++++++++++++
 examples/scale.nim            | 12 ++++++++++++
 src/pixie/fileformats/svg.nim | 23 ++++++++++++++++++++++-
 3 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 examples/data/scale.svg
 create mode 100644 examples/scale.nim

diff --git a/examples/data/scale.svg b/examples/data/scale.svg
new file mode 100644
index 0000000..16dae0e
--- /dev/null
+++ b/examples/data/scale.svg
@@ -0,0 +1,16 @@
+<svg viewBox="-50 -50 100 100" xmlns="http://www.w3.org/2000/svg">
+  <!-- uniform scale -->
+  <circle cx="0" cy="0" r="10" fill="red"
+          transform="scale(4)" />
+
+  <!-- vertical scale -->
+  <circle cx="0" cy="0" r="10" fill="yellow"
+          transform="scale(1,4)" />
+
+  <!-- horizontal scale -->
+  <circle cx="0" cy="0" r="10" fill="pink"
+          transform="scale(4,1)" />
+
+  <!-- No scale -->
+  <circle cx="0" cy="0" r="10" fill="black" />
+</svg>
diff --git a/examples/scale.nim b/examples/scale.nim
new file mode 100644
index 0000000..2003f11
--- /dev/null
+++ b/examples/scale.nim
@@ -0,0 +1,12 @@
+import pixie
+
+let image = newImage(100, 100)
+image.fill(rgba(255, 255, 255, 255))
+
+let flower = readImage("examples/data/scale.svg")
+
+image.draw(
+  flower
+)
+
+image.writeFile("examples/scale.png")
diff --git a/src/pixie/fileformats/svg.nim b/src/pixie/fileformats/svg.nim
index 4465ac9..d3f1769 100644
--- a/src/pixie/fileformats/svg.nim
+++ b/src/pixie/fileformats/svg.nim
@@ -192,6 +192,21 @@ proc decodeCtx(inherited: Ctx, node: XmlNode): Ctx =
         let center = vec2(cx, cy)
         result.transform = result.transform *
           translate(center) * rotate(angle) * translate(-center)
+      elif f.startsWith("scale("):
+        let
+          values =
+            if f.contains(","):
+              f[6 .. ^2].split(",")
+            else:
+              f[6 .. ^2].split(" ")
+        let
+          sx: float32 = parseFloat(values[0].strip())
+          sy: float32 =
+            if values.len > 1:
+              parseFloat(values[1].strip())
+            else:
+              sx
+        result.transform = result.transform * scale(vec2(sx, sy))
       else:
         failInvalidTransform(transform)
 
@@ -348,12 +363,18 @@ proc decodeSvg*(data: string, width = 0, height = 0): Image =
     let
       viewBox = root.attr("viewBox")
       box = viewBox.split(" ")
+      viewBoxMinX = parseInt(box[0])
+      viewBoxMinY= parseInt(box[1])
       viewBoxWidth = parseInt(box[2])
       viewBoxHeight = parseInt(box[3])
 
     var rootCtx = initCtx()
     rootCtx = decodeCtx(rootCtx, root)
 
+    if viewBoxMinX != 0 or viewBoxMinY != 0:
+      rootCtx.transform = rootCtx.transform * translate(
+        vec2(-viewBoxMinX.float32, -viewBoxMinY.float32))
+
     if width == 0 and height == 0: # Default to the view box size
       result = newImage(viewBoxWidth, viewBoxHeight)
     else:
@@ -362,7 +383,7 @@ proc decodeSvg*(data: string, width = 0, height = 0): Image =
       let
         scaleX = width.float32 / viewBoxWidth.float32
         scaleY = height.float32 / viewBoxHeight.float32
-      rootCtx.transform = scale(vec2(scaleX, scaleY))
+      rootCtx.transform = rootCtx.transform * scale(vec2(scaleX, scaleY))
 
     var ctxStack = @[rootCtx]
     for node in root: