Method getTextureDataForText

core/platform/wasm/Device-wasm.cpp:60–192

}

Data Device::getTextureDataForText(std::string_view text,
                                   const FontDefinition& textDefinition,
                                   TextAlign align,
                                   int& width,
                                   int& height,
                                   bool& hasPremultipliedAlpha)
{
    char color[10];
    fmt::format_to_z(color, "#{:02x}{:02x}{:02x}{:02x}", textDefinition._fontFillColor.r, textDefinition._fontFillColor.g,
            textDefinition._fontFillColor.b, textDefinition._fontAlpha);
    // clang-format off
    unsigned char* ptr = (unsigned char*)EM_ASM_PTR({
        var lines = UTF8ToString($0).split("\n");
        var fontName = UTF8ToString($1);
        var fontSize = $2;
        var color = UTF8ToString($3);
        var dimWidth = $4;
        var dimHeight = $5;
        var align = $6;

        // use shared canvas
        var canvas = Module.axmolSharedCanvas = Module.axmolSharedCanvas || document.createElement("canvas");
        var context = canvas.getContext('2d', { willReadFrequently: true });
        context.font = fontSize + "px " + fontName;
        // use alphabetic baseline for text rendering
        context.textBaseline = "alphabetic";

        var linesWidth = [];
        var linesAscent = [];
        var linesDescent = [];
        var totalHeight = 0;
        var maxWidth = dimWidth > 0 ? dimWidth : 0;

        var defaultAscent = 0;
        var defaultDescent = 0;

        var measureDefault = ()=> {
            if (defaultAscent == 0 && defaultDescent == 0) {
                var metrics = context.measureText('M'); // or Hg
                defaultAscent = (typeof metrics.actualBoundingBoxAscent === "number") ? metrics.actualBoundingBoxAscent : fontSize * 0.8;
                defaultDescent = (typeof metrics.actualBoundingBoxDescent === "number") ? metrics.actualBoundingBoxDescent : fontSize * 0.2;
            }
        };

        // compute per line metrics
        for (var i = 0; i < lines.length; i++) {
            var metrics = context.measureText(lines[i]);
            var lineWidth = metrics.width;
            // if browser not support actualBoundingBoxAscent/descent, use fallback values
            var ascent = (typeof metrics.actualBoundingBoxAscent === "number") ? metrics.actualBoundingBoxAscent : fontSize * 0.8;
            var descent = (typeof metrics.actualBoundingBoxDescent === "number") ? metrics.actualBoundingBoxDescent : fontSize * 0.2;
            var lineHeight = ascent + descent;
			// if the line text only contains white space chars, the lineHeight will be 0, 
			// so we re-calculate lineHeight by representative text, i.e. 'M' or 'Hg'
            if (lineHeight == 0) {
                measureDefault();
                ascent = defaultAscent;
                descent = defaultDescent;