Backdrop Polyfill Example

BackdropTemplate.lua

local BackdropTemplatePolyfillMixin = {};

function BackdropTemplatePolyfillMixin:OnBackdropLoaded()
    if not self.backdropInfo then
        return;
    end

    if not self.backdropInfo.edgeFile and not self.backdropInfo.bgFile then
        self.backdropInfo = nil;
        return;
    end

    self:ApplyBackdrop();

    if self.backdropColor then
        local r, g, b = self.backdropColor:GetRGB();
        self:SetBackdropColor(r, g, b, self.backdropColorAlpha or 1);
    end

    if self.backdropBorderColor then
        local r, g, b = self.backdropBorderColor:GetRGB();
        self:SetBackdropBorderColor(r, g, b, self.backdropBorderColorAlpha or 1);
    end

    if self.backdropBorderBlendMode then
        self:SetBackdropBorderBlendMode(self.backdropBorderBlendMode);
    end
end

function BackdropTemplatePolyfillMixin:OnBackdropSizeChanged()
    if self.backdropInfo then
        self:SetupTextureCoordinates();
    end
end

function BackdropTemplatePolyfillMixin:ApplyBackdrop()
    -- The SetBackdrop call will implicitly reset the background and border
    -- texture vertex colors to white, consistent across all client versions.

    self:SetBackdrop(self.backdropInfo);
end

function BackdropTemplatePolyfillMixin:ClearBackdrop()
    self:SetBackdrop(nil);
    self.backdropInfo = nil;
end

function BackdropTemplatePolyfillMixin:GetEdgeSize()
    return self.backdropInfo.edgeSize or 39;
end

function BackdropTemplatePolyfillMixin:HasBackdropInfo(backdropInfo)
    return self.backdropInfo == backdropInfo;
end

function BackdropTemplatePolyfillMixin:SetBorderBlendMode()
    -- Deliberate no-op as the pre-9.x API doesn't support this.
end

function BackdropTemplatePolyfillMixin:SetupPieceVisuals()
    -- Deliberate no-op as backdrop internals are handled C-side pre-9.x.
end

function BackdropTemplatePolyfillMixin:SetupTextureCoordinates()
    -- Deliberate no-op as texture coordinates are handled C-side pre-9.x.
end

AddOn_BackdropTemplateMixin = CreateFromMixins(BackdropTemplateMixin or BackdropTemplatePolyfillMixin);

ADDON_BACKDROP_DIALOG_20_20_5555 = {
    bgFile   = "Interface\\DialogFrame\\UI-DialogBox-Background",
    edgeFile = "Interface\\DialogFrame\\UI-DialogBox-Border",
    tile     = true,
    tileEdge = true,
    tileSize = 20,
    edgeSize = 20,
    insets   = { left = 5, right = 5, top = 5, bottom = 5 },
};

BackdropTemplate.xml

<Ui>
    <Script file="BackdropTemplate.lua"/>

    <Frame name="AddOn_BackdropTemplate" mixin="AddOn_BackdropTemplateMixin" virtual="true">
        <Scripts>
            <OnLoad method="OnBackdropLoaded"/>
            <OnSizeChanged method="OnBackdropSizeChanged"/>
        </Scripts>
    </Frame>

    <!-- Example usage: -->

    <Frame name="TestFrame" parent="UIParent" inherits="AddOn_BackdropTemplate">
        <KeyValues>
            <KeyValue key="backdropInfo" value="ADDON_BACKDROP_DIALOG_20_20_5555" type="global"/>
        </KeyValues>
        <Size x="300" y="300"/>
        <Anchors>
            <Anchor point="CENTER"/>
        </Anchors>
        <Scripts>
            <OnLoad inherit="prepend">
                -- In case you need custom OnLoad behaviour, ensure that
                -- the inherit attribute is specified above.
                print("Loaded!");
            </OnLoad>
        </Scripts>
    </Frame>
</Ui>