Update StateVars only when its widget reports a change (#42)

src/DearImGui.hs

@@ -163,6 +163,8 @@ module DearImGui
   where
 
 -- base
+import Control.Monad
+  ( when )
 import Data.Bool
 import Data.Coerce 
   ( coerce )
@@ -412,6 +414,7 @@ checkbox label ref = liftIO do
     changed <- withCString label \labelPtr ->
       (0 /=) <$> [C.exp| bool { Checkbox($(char* labelPtr), $(bool* boolPtr)) } |]
 
+    when changed do
       newValue <- peek boolPtr
       ref $=! (newValue == 1)
 
@@ -484,6 +487,7 @@ dragFloat desc ref speed minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { DragFloat( $(char* descPtr), $(float *floatPtr), $(float speed'), $(float min'), $(float max')) } |]
 
+    when changed do
       newValue <- peek floatPtr
       ref $=! realToFrac newValue
 
@@ -503,6 +507,7 @@ dragFloat2 desc ref speed minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { DragFloat2( $(char* descPtr), $(float *floatPtr), $(float speed'), $(float min'), $(float max')) } |]
 
+    when changed do
       [x', y'] <- peekArray 2 floatPtr
       ref $=! (realToFrac x', realToFrac y')
 
@@ -522,6 +527,7 @@ dragFloat3 desc ref speed minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { DragFloat3( $(char* descPtr), $(float *floatPtr), $(float speed'), $(float min'), $(float max')) } |]
 
+    when changed do
       [x', y', z'] <- peekArray 3 floatPtr
       ref $=! (realToFrac x', realToFrac y', realToFrac z')
 
@@ -541,6 +547,7 @@ dragFloat4 desc ref speed minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { DragFloat4( $(char* descPtr), $(float *floatPtr), $(float speed'), $(float min'), $(float max')) } |]
 
+    when changed do
       [x', y', z', u'] <- peekArray 4 floatPtr
       ref $=! (realToFrac x', realToFrac y', realToFrac z', realToFrac u')
 
@@ -560,6 +567,7 @@ sliderFloat desc ref minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { SliderFloat( $(char* descPtr), $(float *floatPtr), $(float min'), $(float max')) } |]
 
+    when changed do
       newValue <- peek floatPtr
       ref $=! realToFrac newValue
 
@@ -578,6 +586,7 @@ sliderFloat2 desc ref minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { SliderFloat2( $(char* descPtr), $(float *floatPtr), $(float min'), $(float max')) } |]
 
+    when changed do
       [x', y'] <- peekArray 2 floatPtr
       ref $=! (realToFrac x', realToFrac y')
 
@@ -596,6 +605,7 @@ sliderFloat3 desc ref minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { SliderFloat3( $(char* descPtr), $(float *floatPtr), $(float min'), $(float max')) } |]
 
+    when changed do
       [x', y', z'] <- peekArray 3 floatPtr
       ref $=! (realToFrac x', realToFrac y', realToFrac z')
 
@@ -614,6 +624,7 @@ sliderFloat4 desc ref minValue maxValue = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { SliderFloat4( $(char* descPtr), $(float *floatPtr), $(float min'), $(float max')) } |]
 
+    when changed do
       [x', y', z', u'] <- peekArray 4 floatPtr
       ref $=! (realToFrac x', realToFrac y', realToFrac z', realToFrac u')
 
@@ -648,6 +659,7 @@ colorPicker3 desc ref = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /= ) <$> [C.exp| bool { ColorPicker3( $(char* descPtr), $(float *refPtr) ) } |]
 
+    when changed do
       [x', y', z'] <- peekArray 3 refPtr
       ref $=! ImVec3 (realToFrac x') (realToFrac y') (realToFrac z')
 
@@ -664,6 +676,7 @@ colorButton desc ref = liftIO do
     changed <- withCString desc \descPtr ->
       (0 /=) <$> [C.exp| bool { ColorButton( $(char* descPtr), *$(ImVec4 *refPtr) ) } |]
 
+    when changed do
       newValue <- peek refPtr
       ref $=! newValue