zcatgui/src/render/framebuffer.zig

//! Framebuffer - Pixel buffer for software rendering
//!
//! A simple 2D array of RGBA pixels.
//! The software rasterizer writes to this, then it's blitted to the screen.

const std = @import("std");
const Allocator = std.mem.Allocator;

const Style = @import("../core/style.zig");
const Color = Style.Color;

/// A 2D pixel buffer
pub const Framebuffer = struct {
    allocator: Allocator,
    pixels: []u32,
    width: u32,
    height: u32,

    const Self = @This();

    /// Create a new framebuffer
    pub fn init(allocator: Allocator, width: u32, height: u32) !Self {
        const size = @as(usize, width) * @as(usize, height);
        const pixels = try allocator.alloc(u32, size);
        @memset(pixels, 0);

        return .{
            .allocator = allocator,
            .pixels = pixels,
            .width = width,
            .height = height,
        };
    }

    /// Free the framebuffer
    pub fn deinit(self: Self) void {
        self.allocator.free(self.pixels);
    }

    /// Resize the framebuffer
    pub fn resize(self: *Self, width: u32, height: u32) !void {
        if (width == self.width and height == self.height) return;

        const size = @as(usize, width) * @as(usize, height);
        const new_pixels = try self.allocator.alloc(u32, size);
        @memset(new_pixels, 0);

        self.allocator.free(self.pixels);
        self.pixels = new_pixels;
        self.width = width;
        self.height = height;
    }

    /// Clear the entire buffer to a color
    pub fn clear(self: *Self, color: Color) void {
        const c = color.toABGR();
        @memset(self.pixels, c);
    }

    /// Clear a rectangular region to a color (for partial redraw)
    pub fn clearRect(self: *Self, x: i32, y: i32, w: u32, h: u32, color: Color) void {
        const x_start: u32 = if (x < 0) 0 else @intCast(@min(x, @as(i32, @intCast(self.width))));
        const y_start: u32 = if (y < 0) 0 else @intCast(@min(y, @as(i32, @intCast(self.height))));
        const x_end = @min(x_start + w, self.width);
        const y_end = @min(y_start + h, self.height);

        if (x_start >= x_end or y_start >= y_end) return;

        const c = color.toABGR();
        const row_width = x_end - x_start;

        var py = y_start;
        while (py < y_end) : (py += 1) {
            const row_start = py * self.width + x_start;
            @memset(self.pixels[row_start..][0..row_width], c);
        }
    }

    /// Get pixel at (x, y)
    pub fn getPixel(self: Self, x: i32, y: i32) ?u32 {
        if (x < 0 or y < 0) return null;
        const ux = @as(u32, @intCast(x));
        const uy = @as(u32, @intCast(y));
        if (ux >= self.width or uy >= self.height) return null;

        const idx = uy * self.width + ux;
        return self.pixels[idx];
    }

    /// Set pixel at (x, y)
    pub fn setPixel(self: *Self, x: i32, y: i32, color: Color) void {
        if (x < 0 or y < 0) return;
        const ux = @as(u32, @intCast(x));
        const uy = @as(u32, @intCast(y));
        if (ux >= self.width or uy >= self.height) return;

        const idx = uy * self.width + ux;

        if (color.a == 255) {
            self.pixels[idx] = color.toABGR();
        } else if (color.a > 0) {
            // Blend with existing pixel
            const existing = self.pixels[idx];
            const bg = Color{
                .r = @truncate(existing),
                .g = @truncate(existing >> 8),
                .b = @truncate(existing >> 16),
                .a = @truncate(existing >> 24),
            };
            self.pixels[idx] = color.blend(bg).toABGR();
        }
    }

    /// Draw a filled rectangle
    pub fn fillRect(self: *Self, x: i32, y: i32, w: u32, h: u32, color: Color) void {
        const x_start = @max(0, x);
        const y_start = @max(0, y);
        const x_end = @min(@as(i32, @intCast(self.width)), x + @as(i32, @intCast(w)));
        const y_end = @min(@as(i32, @intCast(self.height)), y + @as(i32, @intCast(h)));

        if (x_start >= x_end or y_start >= y_end) return;

        const c = color.toABGR();

        var py = y_start;
        while (py < y_end) : (py += 1) {
            const row_start = @as(u32, @intCast(py)) * self.width;
            var px = x_start;
            while (px < x_end) : (px += 1) {
                const idx = row_start + @as(u32, @intCast(px));
                if (color.a == 255) {
                    self.pixels[idx] = c;
                } else if (color.a > 0) {
                    const existing = self.pixels[idx];
                    const bg = Color{
                        .r = @truncate(existing),
                        .g = @truncate(existing >> 8),
                        .b = @truncate(existing >> 16),
                        .a = @truncate(existing >> 24),
                    };
                    self.pixels[idx] = color.blend(bg).toABGR();
                }
            }
        }
    }

    /// Draw a rectangle outline
    pub fn drawRect(self: *Self, x: i32, y: i32, w: u32, h: u32, color: Color) void {
        if (w == 0 or h == 0) return;

        // Top and bottom
        self.fillRect(x, y, w, 1, color);
        self.fillRect(x, y + @as(i32, @intCast(h)) - 1, w, 1, color);

        // Left and right
        self.fillRect(x, y + 1, 1, h -| 2, color);
        self.fillRect(x + @as(i32, @intCast(w)) - 1, y + 1, 1, h -| 2, color);
    }

    /// Draw a horizontal line
    pub fn drawHLine(self: *Self, x: i32, y: i32, w: u32, color: Color) void {
        self.fillRect(x, y, w, 1, color);
    }

    /// Draw a vertical line
    pub fn drawVLine(self: *Self, x: i32, y: i32, h: u32, color: Color) void {
        self.fillRect(x, y, 1, h, color);
    }

    /// Draw a line (Bresenham's algorithm)
    pub fn drawLine(self: *Self, x0: i32, y0: i32, x1: i32, y1: i32, color: Color) void {
        var x = x0;
        var y = y0;

        const dx = @abs(x1 - x0);
        const dy = @abs(y1 - y0);
        const sx: i32 = if (x0 < x1) 1 else -1;
        const sy: i32 = if (y0 < y1) 1 else -1;
        var err = @as(i32, @intCast(dx)) - @as(i32, @intCast(dy));

        while (true) {
            self.setPixel(x, y, color);

            if (x == x1 and y == y1) break;

            const e2 = err * 2;
            if (e2 > -@as(i32, @intCast(dy))) {
                err -= @as(i32, @intCast(dy));
                x += sx;
            }
            if (e2 < @as(i32, @intCast(dx))) {
                err += @as(i32, @intCast(dx));
                y += sy;
            }
        }
    }

    /// Get raw pixel data (for blitting to SDL texture)
    pub fn getData(self: Self) []const u32 {
        return self.pixels;
    }

    /// Get pitch in bytes
    pub fn getPitch(self: Self) u32 {
        return self.width * 4;
    }
};

// =============================================================================
// Tests
// =============================================================================

test "Framebuffer basic" {
    var fb = try Framebuffer.init(std.testing.allocator, 100, 100);
    defer fb.deinit();

    fb.clear(Color.black);
    fb.setPixel(50, 50, Color.white);

    const pixel = fb.getPixel(50, 50);
    try std.testing.expect(pixel != null);
}

test "Framebuffer fillRect" {
    var fb = try Framebuffer.init(std.testing.allocator, 100, 100);
    defer fb.deinit();

    fb.clear(Color.black);
    fb.fillRect(10, 10, 20, 20, Color.red);

    // Check inside
    const inside = fb.getPixel(15, 15);
    try std.testing.expect(inside != null);
    try std.testing.expectEqual(Color.red.toABGR(), inside.?);

    // Check outside
    const outside = fb.getPixel(5, 5);
    try std.testing.expect(outside != null);
    try std.testing.expectEqual(Color.black.toABGR(), outside.?);
}

test "Framebuffer out of bounds" {
    var fb = try Framebuffer.init(std.testing.allocator, 100, 100);
    defer fb.deinit();

    // These should not crash
    fb.setPixel(-1, 50, Color.white);
    fb.setPixel(50, -1, Color.white);
    fb.setPixel(100, 50, Color.white);
    fb.setPixel(50, 100, Color.white);

    try std.testing.expect(fb.getPixel(-1, 50) == null);
}