style setter: add Add method

StyleSetter.go

@@ -37,6 +37,46 @@ func Style() *StyleSetter {
 	return &ss
 }
 
+// Add merges two StyleSetters.
+// Add puts other "on top" of ss, meaning, "other" is applied after "ss".
+// e.g. if both StyleSetters set imgui.StyleVarAlpha, the value from "other" will be used.
+// NOTE: font value "nil" is treated as "not set" and will not be changed if declared by other.
+// NOTE: true is preffered over false for disabled field.
+// NOTE: layout field will be reset.
+func (ss *StyleSetter) Add(other *StyleSetter) *StyleSetter {
+	if other == nil {
+		return ss
+	}
+
+	for k, v := range other.colors {
+		ss.colors[k] = v
+	}
+
+	for k, v := range other.styles {
+		ss.styles[k] = v
+	}
+
+	for k, v := range other.plotColors {
+		ss.plotColors[k] = v
+	}
+
+	for k, v := range other.plotStyles {
+		ss.plotStyles[k] = v
+	}
+
+	if other.font != nil {
+		ss.font = other.font
+	}
+
+	if other.disabled {
+		ss.disabled = true
+	}
+
+	ss.layout = nil
+
+	return ss
+}
+
 // SetColor sets colorID's color.
 func (ss *StyleSetter) SetColor(colorID StyleColorID, col color.Color) *StyleSetter {
 	ss.colors[colorID] = col

StyleSetter_test.go

@@ -0,0 +1,53 @@
+package giu
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"golang.org/x/image/colornames"
+)
+
+func TestStyleSetter_Add(t *testing.T) {
+	cases := []struct {
+		name     string
+		setter   *StyleSetter
+		other    *StyleSetter
+		expected *StyleSetter
+	}{
+		{
+			name: "Adding nil",
+			setter: Style().SetColor(StyleColorText, colornames.Red).
+				SetStyle(StyleVarWindowPadding, 10, 10),
+			other: nil,
+			expected: Style().SetColor(StyleColorText, colornames.Red).
+				SetStyle(StyleVarWindowPadding, 10, 10),
+		},
+		{
+			name: "Adding some styles/colors",
+			setter: Style().SetColor(StyleColorText, colornames.Red).
+				SetStyle(StyleVarWindowPadding, 10, 10),
+			other: Style().SetColor(StyleColorWindowBg, colornames.Red).
+				SetStyle(StyleVarFramePadding, 10, 10),
+			expected: Style().SetColor(StyleColorText, colornames.Red).
+				SetStyle(StyleVarWindowPadding, 10, 10).
+				SetColor(StyleColorWindowBg, colornames.Red).
+				SetStyle(StyleVarFramePadding, 10, 10),
+		},
+		{
+			name: "Overwrite",
+			setter: Style().SetColor(StyleColorText, colornames.Red).
+				SetStyle(StyleVarWindowPadding, 10, 10),
+			other: Style().SetColor(StyleColorText, colornames.Blue).
+				SetStyle(StyleVarWindowPadding, 11, 11),
+			expected: Style().SetColor(StyleColorText, colornames.Blue).
+				SetStyle(StyleVarWindowPadding, 11, 11),
+		},
+	}
+
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			c.setter.Add(c.other)
+			assert.True(t, assert.ObjectsAreEqual(c.setter, c.expected), "Expected: %v, got: %v", c.expected, c.setter)
+		})
+	}
+}