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Add duck_engine example generated by Grok 3
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‎Makefile

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@@ -56,3 +56,7 @@ hello_sdl:: all
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bullet_engine:: all
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erlc -o examples/bullet_engine examples/bullet_engine/*.erl
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cd examples/bullet_engine && ./start.sh
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duck_engine: all
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erlc -o examples/duck_engine examples/duck_engine/*.erl
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cd examples/duck_engine && ./start.sh

‎examples/duck_engine/duck_engine.erl

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%% This is an example. Feel free to copy and reuse as you wish.
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%%
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%% This example was almost entirely generated by Grok 3 with
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%% minor human-driven changes (such as fixing the position of
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%% legs). The raster is imperfect, either missing sides or
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%% sides being incorrectly defined.
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%%
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%% The conversation leading to this example can be found at
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%% https://x.com/i/grok/share/IN1mWW5a4g1zcqYTInA4X8BXP
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-module(duck_engine).
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-export([run/0]).
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run() ->
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% Initialize SDL with video subsystem
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case sdl:start([video]) of
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ok ->
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% Ensure SDL stops when this process exits
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sdl:stop_on_exit(),
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% Create a window (title, x, y, width, height, flags)
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{ok, Window} = sdl_window:create(<<"Duck Engine">>, 100, 100, 800, 600, []),
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% Create a renderer with acceleration and vsync
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{ok, Renderer} = sdl_renderer:create(Window, -1, [accelerated, present_vsync]),
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% Define initial duck vertices
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Duck = duck_vertices(),
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% Start the rendering loop with initial rotation angles
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loop(Window, Renderer, Duck, {0.0, 0.0, 0.0});
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{application_start_error, Reason} ->
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io:format("Failed to start esdl2 application: ~p~n", [Reason]),
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error;
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{error, String} ->
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io:format("SDL initialization failed: ~s~n", [String]),
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error
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end.
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% Main rendering loop
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loop(Window, Renderer, Duck, {XAngle, YAngle, ZAngle}) ->
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% Set clear color to white (R, G, B, A)
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sdl_renderer:set_draw_color(Renderer, 255, 255, 255, 255),
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% Clear the renderer
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sdl_renderer:clear(Renderer),
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% Rotate the duck vertices
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RotatedDuck = rotate_duck(Duck, XAngle, YAngle, ZAngle),
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% Project and draw the rotated duck
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project_and_draw(RotatedDuck, Renderer),
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% Present the rendered frame
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sdl_renderer:present(Renderer),
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% Process all events and determine if we should quit
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case handle_events() of
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quit -> ok; % Exit if quit event is detected
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continue ->
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% Sleep for ~16ms (approx 60 FPS) and continue with updated angles
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timer:sleep(16),
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loop(Window, Renderer, Duck, {XAngle + 0.03, YAngle + 0.05, ZAngle + 0.04})
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end.
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% Handle all pending events in the queue
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handle_events() ->
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case sdl_events:poll() of
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#{type := quit} -> quit; % Quit event detected
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#{type := _} -> handle_events(); % Other event, keep processing
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false -> continue % No more events, proceed with rendering
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end.
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% Rotate duck vertices around X, Y, and Z axes
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rotate_duck(Vertices, XAngle, YAngle, ZAngle) ->
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RotX = matrix3d:rotate_x(XAngle),
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RotY = matrix3d:rotate_y(YAngle),
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RotZ = matrix3d:rotate_z(ZAngle),
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% Combine rotation matrices: X * (Y * Z)
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TempMatrix = matrix3d:multiply(RotY, RotZ),
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CombinedMatrix = matrix3d:multiply(RotX, TempMatrix),
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[matrix3d:apply(CombinedMatrix, Vertex) || Vertex <- Vertices].
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% Define duck vertices (unchanged from your description)
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duck_vertices() ->
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[
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% Body: 0-11
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{1.0, 1.4, 0.8}, {1.0, 1.4, -0.8}, {1.4, 0.6, 0.8}, {1.4, 0.6, -0.8},
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{1.0, -1.0, 0.8}, {1.0, -1.0, -0.8}, {-1.0, 1.4, 0.8}, {-1.0, 1.4, -0.8},
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{-1.4, 0.6, 0.8}, {-1.4, 0.6, -0.8}, {-1.0, -1.0, 0.8}, {-1.0, -1.0, -0.8},
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% Head: 12-19
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{-1.4, 2.0, 0.6}, {-1.4, 2.0, -0.6}, {-1.4, 1.2, 0.6}, {-1.4, 1.2, -0.6},
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{-2.0, 2.0, 0.6}, {-2.0, 2.0, -0.6}, {-2.0, 1.2, 0.6}, {-2.0, 1.2, -0.6},
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% Beak: 20-25
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{-2.4, 1.8, 0.2}, {-2.4, 1.8, -0.2}, {-2.4, 1.4, 0.2}, {-2.4, 1.4, -0.2},
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{-2.0, 1.6, 0.2}, {-2.0, 1.6, -0.2},
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% Right Leg: 26-29
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{-1.0, -1.0, -0.3}, {-1.0, -2.0, -0.3}, {-1.2, -2.0, -0.1}, {-1.2, -2.0, -0.5},
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% Left Leg: 30-33
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{-1.0, -1.0, 0.3}, {-1.0, -2.0, 0.3}, {-1.2, -2.0, 0.1}, {-1.2, -2.0, 0.5}
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].
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% Project 3D vertices to 2D and draw filled triangles
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project_and_draw(Vertices, Renderer) ->
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Projected = [project_vertex(V) || V <- Vertices],
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% Body - Front (bright yellow)
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sdl_renderer:set_draw_color(Renderer, 255, 255, 0, 255),
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FrontTriangles = [
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[0, 2, 4], [6, 8, 10], [0, 6, 10], [0, 4, 10]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- FrontTriangles],
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% Body - Back (darker yellow)
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sdl_renderer:set_draw_color(Renderer, 220, 220, 0, 255),
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BackTriangles = [
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[1, 3, 5], [7, 9, 11], [1, 7, 11], [1, 5, 11]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- BackTriangles],
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% Body - Right (golden yellow)
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sdl_renderer:set_draw_color(Renderer, 255, 215, 0, 255),
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RightTriangles = [
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[0, 1, 3], [3, 5, 4], [0, 2, 4]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- RightTriangles],
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% Body - Left (pale yellow)
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sdl_renderer:set_draw_color(Renderer, 255, 245, 0, 255),
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LeftTriangles = [
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[6, 7, 9], [9, 11, 10], [6, 8, 10]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- LeftTriangles],
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% Body - Top (light yellow)
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sdl_renderer:set_draw_color(Renderer, 255, 255, 100, 255),
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TopTriangles = [
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[0, 1, 6], [1, 7, 6]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- TopTriangles],
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% Body - Bottom (deep yellow)
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sdl_renderer:set_draw_color(Renderer, 255, 200, 0, 255),
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BottomTriangles = [
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[4, 5, 10], [5, 11, 10]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- BottomTriangles],
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% Neck (match head color: slightly greenish yellow)
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sdl_renderer:set_draw_color(Renderer, 245, 255, 0, 255),
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NeckTriangles = [
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[6, 7, 18], [7, 19, 18], % Left-back to head bottom
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[0, 1, 14], [1, 15, 14] % Right-front to head bottom
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- NeckTriangles],
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% Head (slightly greenish yellow)
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sdl_renderer:set_draw_color(Renderer, 245, 255, 0, 255),
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HeadTriangles = [
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[12, 13, 15], [12, 14, 15], [16, 17, 19], [16, 18, 19],
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[12, 16, 18], [12, 14, 18], [13, 17, 19], [13, 15, 19]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- HeadTriangles],
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% Beak (orange-yellow)
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sdl_renderer:set_draw_color(Renderer, 255, 235, 0, 255),
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BeakTriangles = [
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[20, 21, 23], [20, 22, 23], [20, 24, 25], [20, 21, 25],
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[22, 24, 25], [22, 23, 25]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- BeakTriangles],
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% Legs (muted yellow)
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sdl_renderer:set_draw_color(Renderer, 235, 235, 0, 255),
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LegTriangles = [
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[26, 27, 28], [26, 27, 29], [30, 31, 32], [30, 31, 33]
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],
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[fill_triangle(Renderer, [lists:nth(A+1, Projected) || A <- Tri]) || Tri <- LegTriangles],
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% Draw edges in black
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sdl_renderer:set_draw_color(Renderer, 0, 0, 0, 255),
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Edges = [
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{0, 1}, {1, 3}, {3, 5}, {5, 4}, {4, 2}, {2, 0},
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{6, 7}, {7, 9}, {9, 11}, {11, 10}, {10, 8}, {8, 6},
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{0, 6}, {1, 7}, {2, 8}, {3, 9}, {4, 10}, {5, 11},
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{12, 13}, {13, 15}, {15, 14}, {14, 12},
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{16, 17}, {17, 19}, {19, 18}, {18, 16},
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{12, 16}, {13, 17}, {14, 18}, {15, 19},
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{6, 16}, {7, 17}, {8, 18}, {9, 19},
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{20, 21}, {21, 23}, {23, 22}, {22, 20},
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{20, 24}, {21, 25}, {22, 24}, {23, 25}, {24, 25},
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{16, 24}, {17, 25},
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{26, 27}, {27, 28}, {27, 29},
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{30, 31}, {31, 32}, {31, 33}
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],
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[draw_line(Renderer, lists:nth(A+1, Projected), lists:nth(B+1, Projected)) || {A, B} <- Edges].
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% Project a 3D vertex to 2D screen coordinates (unchanged)
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project_vertex({X, Y, Z}) ->
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ZOffset = Z + 10,
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Scale = 800,
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ScreenX = 400 + round((X / ZOffset) * Scale),
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ScreenY = 300 + round((Y / ZOffset) * Scale),
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{ScreenX, ScreenY}.
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% Draw a line (unchanged)
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draw_line(Renderer, {X1, Y1}, {X2, Y2}) ->
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sdl_renderer:draw_line(Renderer, X1, Y1, X2, Y2).
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% Fill a triangle with scanline approach, handling degenerate cases
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fill_triangle(Renderer, Points) ->
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[{X1, Y1}, {X2, Y2}, {X3, Y3}] = lists:sort(fun({_, YA}, {_, YB}) -> YA =< YB end, Points),
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if
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Y1 == Y3 -> % Degenerate case: all Ys equal
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if
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X1 == X2 andalso X2 == X3 -> ok; % Single point
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true ->
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XMin = lists:min([X1, X2, X3]),
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XMax = lists:max([X1, X2, X3]),
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sdl_renderer:draw_line(Renderer, XMin, Y1, XMax, Y1)
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end;
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true ->
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case {Y1 == Y2, Y2 == Y3} of
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{true, false} -> % Flat top
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fill_flat_top_triangle(Renderer, X1, Y1, X2, Y2, X3, Y3);
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{false, true} -> % Flat bottom
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fill_flat_bottom_triangle(Renderer, X1, Y1, X2, Y2, X3, Y3);
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{false, false} -> % General case
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T = (Y2 - Y1) / (Y3 - Y1),
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XMid = X1 + round(T * (X3 - X1)),
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fill_flat_bottom_triangle(Renderer, X1, Y1, X2, Y2, XMid, Y2),
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fill_flat_top_triangle(Renderer, X2, Y2, XMid, Y2, X3, Y3)
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end
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end.
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% Fill a flat-bottom triangle
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fill_flat_bottom_triangle(Renderer, X1, Y1, X2, Y2, X3, _) ->
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lists:foreach(
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fun(Y) ->
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T = (Y - Y1) / (Y2 - Y1),
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XA = X1 + round(T * (X2 - X1)),
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XB = X1 + round(T * (X3 - X1)),
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{XStart, XEnd} = if XA =< XB -> {XA, XB}; true -> {XB, XA} end,
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sdl_renderer:draw_line(Renderer, XStart, Y, XEnd, Y)
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end,
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lists:seq(round(Y1), round(Y2))
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).
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% Fill a flat-top triangle
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fill_flat_top_triangle(Renderer, X1, Y1, X2, _, X3, Y3) ->
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lists:foreach(
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fun(Y) ->
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T = (Y - Y1) / (Y3 - Y1),
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XA = X1 + round(T * (X3 - X1)),
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XB = X2 + round(T * (X3 - X2)),
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{XStart, XEnd} = if XA =< XB -> {XA, XB}; true -> {XB, XA} end,
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sdl_renderer:draw_line(Renderer, XStart, Y, XEnd, Y)
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end,
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lists:seq(round(Y1), round(Y3))
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).

‎examples/duck_engine/matrix3d.erl

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%% This is an example. Feel free to copy and reuse as you wish.
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-module(matrix3d).
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-export([rotate_x/1, rotate_y/1, rotate_z/1, multiply/2, apply/2]).
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% Rotation matrix around X-axis (angle in radians)
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rotate_x(Angle) ->
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Cos = math:cos(Angle),
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Sin = math:sin(Angle),
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[[1, 0, 0 ],
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[0, Cos, -Sin ],
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[0, Sin, Cos]].
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% Rotation matrix around Y-axis
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rotate_y(Angle) ->
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Cos = math:cos(Angle),
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Sin = math:sin(Angle),
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[[ Cos, 0, Sin ],
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[ 0, 1, 0 ],
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[-Sin, 0, Cos]].
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% Rotation matrix around Z-axis
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rotate_z(Angle) ->
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Cos = math:cos(Angle),
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Sin = math:sin(Angle),
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[[Cos, -Sin, 0 ],
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[Sin, Cos, 0 ],
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[0, 0, 1]].
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% Multiply two 3x3 matrices
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multiply(A, B) ->
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[[A11, A12, A13],
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[A21, A22, A23],
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[A31, A32, A33]] = A,
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[[B11, B12, B13],
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[B21, B22, B23],
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[B31, B32, B33]] = B,
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[[A11*B11 + A12*B21 + A13*B31, A11*B12 + A12*B22 + A13*B32, A11*B13 + A12*B23 + A13*B33],
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[A21*B11 + A22*B21 + A23*B31, A21*B12 + A22*B22 + A23*B32, A21*B13 + A22*B23 + A23*B33],
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[A31*B11 + A32*B21 + A33*B31, A31*B12 + A32*B22 + A33*B32, A31*B13 + A32*B23 + A33*B33]].
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% Apply a 3x3 matrix to a 3D vertex {X, Y, Z}
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apply(Matrix, {X, Y, Z}) ->
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[[M11, M12, M13],
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[M21, M22, M23],
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[M31, M32, M33]] = Matrix,
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NewX = M11 * X + M12 * Y + M13 * Z,
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NewY = M21 * X + M22 * Y + M23 * Z,
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NewZ = M31 * X + M32 * Y + M33 * Z,
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{NewX, NewY, NewZ}.

‎examples/duck_engine/start.sh

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#!/bin/sh
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erl -smp enable +stbt db -pa ../../ebin -eval "duck_engine:run()."

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