zcatpdf/examples/transparency_demo.zig

//! Transparency Demo - Alpha/Opacity Support
//!
//! Demonstrates the transparency capabilities of zpdf including:
//! - Fill opacity for shapes and text
//! - Stroke opacity for lines and outlines
//! - Layered transparent objects

const std = @import("std");
const pdf = @import("zpdf");

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    std.debug.print("zpdf - Transparency Demo\n", .{});

    var doc = pdf.Pdf.init(allocator, .{});
    defer doc.deinit();

    doc.setTitle("Transparency Demo");
    doc.setAuthor("zpdf");

    const page = try doc.addPage(.{});

    // Title
    try page.setFont(.helvetica_bold, 24);
    page.setFillColor(pdf.Color.rgb(41, 98, 255));
    try page.drawText(50, 780, "Transparency / Alpha");

    try page.setFont(.helvetica, 11);
    page.setFillColor(pdf.Color.black);
    try page.drawText(50, 755, "Demonstrating fill and stroke opacity using ExtGState");

    // =========================================================================
    // Fill Opacity Examples
    // =========================================================================
    try page.setFont(.helvetica_bold, 14);
    page.setFillColor(pdf.Color.black);
    try page.drawText(50, 710, "Fill Opacity:");

    // Draw overlapping squares with different opacities
    const base_x: f32 = 80;
    const base_y: f32 = 550;
    const size: f32 = 100;

    // First layer - red square (fully opaque)
    page.setFillColor(pdf.Color.rgb(255, 0, 0));
    try page.fillRect(base_x, base_y, size, size);

    // Second layer - green square (75% opacity)
    page.setFillColor(pdf.Color.rgb(0, 255, 0));
    try page.setFillOpacity(0.75);
    try page.fillRect(base_x + 40, base_y + 30, size, size);

    // Third layer - blue square (50% opacity)
    page.setFillColor(pdf.Color.rgb(0, 0, 255));
    try page.setFillOpacity(0.5);
    try page.fillRect(base_x + 80, base_y + 60, size, size);

    // Labels
    try page.setOpacity(1.0); // Reset to fully opaque
    try page.setFont(.helvetica, 9);
    page.setFillColor(pdf.Color.dark_gray);
    try page.drawText(base_x, base_y - 15, "Overlapping (100%, 75%, 50%)");

    // Individual opacity examples
    const opacities = [_]f32{ 1.0, 0.75, 0.5, 0.25, 0.1 };
    var x: f32 = 280;

    for (opacities) |opacity| {
        try page.setFillOpacity(opacity);
        page.setFillColor(pdf.Color.rgb(128, 0, 128)); // Purple
        try page.fillRect(x, base_y + 30, 60, 60);

        try page.setOpacity(1.0); // Reset for label
        try page.setFont(.helvetica, 9);
        page.setFillColor(pdf.Color.dark_gray);

        var buf: [32]u8 = undefined;
        const label = std.fmt.bufPrint(&buf, "{d}%", .{@as(u32, @intFromFloat(opacity * 100))}) catch "??";
        try page.drawText(x + 20, base_y + 10, label);

        x += 70;
    }

    // =========================================================================
    // Stroke Opacity Examples
    // =========================================================================
    try page.setOpacity(1.0);
    try page.setFont(.helvetica_bold, 14);
    page.setFillColor(pdf.Color.black);
    try page.drawText(50, 500, "Stroke Opacity:");

    try page.setLineWidth(8);
    page.setStrokeColor(pdf.Color.rgb(220, 20, 60)); // Crimson

    x = 80;
    for (opacities) |opacity| {
        try page.setStrokeOpacity(opacity);
        try page.drawLine(x, 420, x + 80, 420);

        try page.setOpacity(1.0);
        try page.setFont(.helvetica, 9);
        page.setFillColor(pdf.Color.dark_gray);

        var buf: [32]u8 = undefined;
        const label = std.fmt.bufPrint(&buf, "{d}%", .{@as(u32, @intFromFloat(opacity * 100))}) catch "??";
        try page.drawText(x + 20, 400, label);

        x += 100;
    }

    // =========================================================================
    // Combined Fill and Stroke Opacity
    // =========================================================================
    try page.setOpacity(1.0);
    try page.setFont(.helvetica_bold, 14);
    page.setFillColor(pdf.Color.black);
    try page.drawText(50, 370, "Combined Fill + Stroke Opacity:");

    try page.setLineWidth(4);

    x = 80;
    const fill_opacities = [_]f32{ 1.0, 0.5, 0.25 };
    const stroke_opacities = [_]f32{ 1.0, 0.5, 0.25 };

    for (fill_opacities, stroke_opacities) |fill_op, stroke_op| {
        page.setFillColor(pdf.Color.rgb(100, 149, 237)); // Cornflower blue
        page.setStrokeColor(pdf.Color.rgb(0, 0, 139)); // Dark blue

        try page.setFillOpacity(fill_op);
        try page.setStrokeOpacity(stroke_op);

        try page.drawFilledRect(x, 280, 80, 60);

        try page.setOpacity(1.0);
        try page.setFont(.helvetica, 8);
        page.setFillColor(pdf.Color.dark_gray);

        var buf: [32]u8 = undefined;
        const label = std.fmt.bufPrint(&buf, "f:{d}% s:{d}%", .{
            @as(u32, @intFromFloat(fill_op * 100)),
            @as(u32, @intFromFloat(stroke_op * 100)),
        }) catch "??";
        try page.drawText(x, 265, label);

        x += 120;
    }

    // =========================================================================
    // Transparent Text
    // =========================================================================
    try page.setOpacity(1.0);
    try page.setFont(.helvetica_bold, 14);
    page.setFillColor(pdf.Color.black);
    try page.drawText(50, 230, "Transparent Text:");

    // Background rectangle
    page.setFillColor(pdf.Color.rgb(255, 215, 0)); // Gold
    try page.fillRect(80, 130, 450, 70);

    // Overlapping text with different opacities
    try page.setFont(.helvetica_bold, 48);

    page.setFillColor(pdf.Color.rgb(255, 0, 0));
    try page.setFillOpacity(1.0);
    try page.drawText(100, 150, "ZPDF");

    page.setFillColor(pdf.Color.rgb(0, 128, 0));
    try page.setFillOpacity(0.6);
    try page.drawText(150, 160, "ZPDF");

    page.setFillColor(pdf.Color.rgb(0, 0, 255));
    try page.setFillOpacity(0.3);
    try page.drawText(200, 170, "ZPDF");

    // =========================================================================
    // Transparent Circles (Venn diagram style)
    // =========================================================================
    try page.setOpacity(1.0);
    try page.setFont(.helvetica_bold, 14);
    page.setFillColor(pdf.Color.black);
    try page.drawText(350, 230, "Overlapping Circles:");

    try page.setFillOpacity(0.5);

    page.setFillColor(pdf.Color.rgb(255, 0, 0));
    try page.fillCircle(420, 170, 50);

    page.setFillColor(pdf.Color.rgb(0, 255, 0));
    try page.fillCircle(460, 170, 50);

    page.setFillColor(pdf.Color.rgb(0, 0, 255));
    try page.fillCircle(440, 130, 50);

    // Footer
    try page.setOpacity(1.0);
    try page.setFont(.helvetica, 9);
    page.setFillColor(pdf.Color.medium_gray);
    try page.drawText(250, 50, "zpdf Transparency Demo");

    // Save
    const filename = "transparency_demo.pdf";
    try doc.save(filename);

    std.debug.print("Created: {s} ({d} pages)\n", .{ filename, doc.pageCount() });
    std.debug.print("Done!\n", .{});
}