usg/src/Renderer.zig

const std = @import("std");
const sdl = @import("sdl2");
const gl = @import("zgl");

const Self = @This();

window: sdl.Window,
context: sdl.gl.Context,
color_loc: u32,
buffer: gl.Buffer,
color: [4]f32,

pub fn init() !Self {
    try sdl.init(.{ .video = true, .audio = true, .events = true });

    // Set OpenGL version
    try sdl.gl.setAttribute(.{ .context_major_version = 3 });
    try sdl.gl.setAttribute(.{ .context_minor_version = 3 });

    const window = try sdl.createWindow(
        "USG",
        .{ .centered = {} },
        .{ .centered = {} },
        1280,
        720,
        .{ .opengl = true, .shown = true }
    );

    const ctx = try sdl.gl.createContext(window);

    var color_loc: u32 = undefined;
    const program = gl.Program.create();
    {
        const vs = gl.Shader.create(.vertex);
        defer vs.delete();
        vs.source(1, &.{@embedFile("shaders/vector.vs")});
        vs.compile();
        const fs = gl.Shader.create(.fragment);
        defer fs.delete();
        fs.source(1, &.{@embedFile("shaders/fragment.fs")});
        fs.compile();
        program.attach(vs);
        defer program.detach(vs);
        program.attach(fs);
        defer program.detach(fs);
        program.link();
        color_loc = program.uniformLocation("color").?;
    }
    program.use();

    var vertex_array = gl.VertexArray.gen();
    vertex_array.bind();

    const buf = gl.Buffer.gen();
    buf.bind(.array_buffer);

    gl.clearColor(0.91, 0.97, 1.00, 1.00);

    return Self{
        .window = window,
        .context = ctx,
        .color_loc = color_loc,
        .buffer = buf,
        .color = .{0,0,0,0}
    };
}

pub fn render(self: Self) void {
    sdl.gl.swapWindow(self.window);

    gl.clear(.{ .color = true });
}

pub fn deinit(self: Self) void {
    sdl.quit();
    self.window.destroy();
    sdl.gl.deleteContext(self.context);
}

pub fn setColor(self: *Self, r: u8, g: u32, b: u32, a: u32) void {
    self.*.color = .{
        @intToFloat(f32, r)/255.0,
        @intToFloat(f32, g)/255.0,
        @intToFloat(f32, b)/255.0,
        @intToFloat(f32, a)/255.0,
    };
}

pub fn drawRectangle(self: *Self, x: u32, y: u32, w: u32, h: u32) void {
    var wsize = self.window.getSize();

    var xunit = 2 / @intToFloat(f32, wsize.width);
    var yunit = 2 / @intToFloat(f32, wsize.height);

    var xf = @intToFloat(f32, x) * xunit - 1;
    var yf = 1 - @intToFloat(f32, y) * yunit;
    var wf = @intToFloat(f32, w) * xunit;
    var hf = @intToFloat(f32, h) * yunit;

    gl.enableVertexAttribArray(0);
    gl.vertexAttribPointer(0, 3, .float, false, 0, 0);

    std.debug.print("{} {}\n", .{ xf, yf });
    const vertex_buffer = [_]f32{
        xf,      yf,      0.0,
        xf + wf, yf,      0.0,
        xf,      yf + hf, 0.0,
    };

    self.buffer.data(f32, &vertex_buffer, .static_draw);

    gl.uniform4fv(self.color_loc, &.{ self.color });
    gl.drawArrays(.triangles, 0, 3);

    gl.disableVertexAttribArray(0);

    _ = xf;
    _ = yf;
}