Fixes #615 - Bug in zoom calculation

imageflow_core/tests/visuals.rs

@@ -1068,6 +1068,25 @@ fn test_crop_with_preshrink() {
 
 }
 
+#[test]
+fn test_zoom_with_preshrink() {
+
+    //Certain dimensions of images would trigger preshrinking and also break zoom calculation
+    let steps = vec![
+        Node::CommandString{
+            kind: CommandStringKind::ImageResizer4,
+            value: "zoom=0.25".to_owned(),
+            decode: Some(0),
+            encode: None,
+            watermarks: None
+        }
+        ];
+    let (w, _h) = get_result_dimensions(&steps, vec![ IoTestEnum::Url("https://imageflow-resources.s3.us-west-2.amazonaws.com/test_inputs/5760_x_4320.jpg".to_owned())], false);
+    assert_eq!(w, 1440);
+
+}
+
+
 #[test]
 fn webp_lossless_alpha_decode_and_scale() {
     let matched = compare(Some(IoTestEnum::Url("https://imageflow-resources.s3-us-west-2.amazonaws.com/test_inputs/1_webp_ll.webp".to_owned())), 500,

imageflow_riapi/src/ir4/layout.rs

@@ -9,7 +9,9 @@ use imageflow_types::{ConstraintMode, ConstraintGravity, WatermarkConstraintBox,
 
 pub struct Ir4Layout{
     i: Instructions,
+    /// The actual, not-pre-shrunk image width. May differ from the bitmap size during IDCT scaling
     reference_width: i32,
+    /// The actual, not-pre-shrunk image height. May differ from the bitmap size during IDCT scaling
     reference_height: i32,
     /// source width
     w: i32,
@@ -40,6 +42,11 @@ impl Ir4Layout{
     }
 
 
+    fn get_preshrink_ratio(&self) ->f64{
+        return f64::from(self.w) / f64::from(self.reference_width)
+    }
+
+
 
     fn get_precrop(&self) -> (i32,i32){
         if((self.i.srotate.unwrap_or(0) / 90 + 4) % 2) == 0 {
@@ -82,12 +89,16 @@ impl Ir4Layout{
         Ok((if w < 1 { None } else { Some(w) }, if h < 1 { None } else { Some(h)}))
     }
 
-    fn get_ideal_target_size(&self, source: AspectRatio) -> sizing::Result<AspectRatio>{
+    fn get_ideal_target_size(&self, source: AspectRatio, preshrink_ratio: f64) -> sizing::Result<AspectRatio>{
 
+        // When no w/h is specified, we should apply zoom relative to the original image dimensions. 
+        let unshrunk_w = (f64::from(source.w) / preshrink_ratio) as i32;
+        let unshrunk_h = (f64::from(source.h) / preshrink_ratio) as i32;
+
 
         let (w,h) = match self.get_wh_from_all(source)? {
             (Some(w), Some(h)) => (w,h),
-            (None, None) => (source.w, source.h),
+            (None, None) => (unshrunk_w, unshrunk_h),
             (Some(w), None) => (w, source.height_for(w, None)?),
             (None, Some(h)) => (source.width_for(h, None)?,h)
         };
@@ -291,7 +302,7 @@ impl Ir4Layout{
 
         let initial_size = AspectRatio::create(source_w, source_h)?;
 
-        let target = ir_layout.get_ideal_target_size(initial_size)?;
+        let target = ir_layout.get_ideal_target_size(initial_size, ir_layout.get_preshrink_ratio())?;
 
         let constraints = ir_layout.build_constraints();
 
@@ -353,7 +364,7 @@ impl Ir4Layout{
 
         let initial_size = sizing::AspectRatio::create(initial_crop[2] - initial_crop[0], initial_crop[3] - initial_crop[1])?;
 
-        let target = self.get_ideal_target_size(initial_size)?;
+        let target = self.get_ideal_target_size(initial_size, self.get_preshrink_ratio())?;
 
         let constraints = self.build_constraints();
 

imageflow_riapi/src/ir4/mod.rs

@@ -140,7 +140,9 @@ impl Ir4SourceFrameInfo{
 pub struct Ir4Expand{
     pub i: Ir4Command,
     pub source: Ir4SourceFrameInfo,
+    /// The actual, not-pre-shrunk image width. May differ from the bitmap size during IDCT scaling
     pub reference_width: i32,
+    /// The actual, not-pre-shrunk image height. May differ from the bitmap size during IDCT scaling
     pub reference_height: i32,
     pub encode_id: Option<i32>,
     pub watermarks: Option<Vec<imageflow_types::Watermark>>