Flood fill chapter (#738)

* adding rough draft of flood fill chapter

* adding video to chapter

Author: leios

SUMMARY.md

@@ -36,5 +36,7 @@
         * [Split-Operator Method](contents/split-operator_method/split-operator_method.md)
 * [Data Compression](contents/data_compression/data_compression.md)
     * [Huffman Encoding](contents/huffman_encoding/huffman_encoding.md)
+* [Computer Graphics](contents/computer_graphics/computer_graphics.md)
+    * [Flood Fill](contents/flood_fill/flood_fill.md)
 * [Quantum Information](contents/quantum_information/quantum_information.md)
 * [Computus](contents/computus/computus.md)

contents/computer_graphics/computer_graphics.md

@@ -0,0 +1,17 @@
+# Computer Graphics
+
+Of all areas of computer science research, none have had more of an immediate impact on multimedia than computer graphics.
+This sub-field is distinctly different than computational science in that it focuses on the *appearance* of realistic details, instead of computing those details precisely.
+Where a computational scientist might spend years writing software that runs on the fastest computers known to man to simulate climate, the computer graphics researcher might apply machine learning to create fluid simulations that look good enough to the untrained eye.
+In the end, the computational scientist will have a plot and the computer graphics researcher will have a beautifully rendered simulation.
+
+Though I may have painted computer graphics to be a bit hand-wavey, that could not be further from the truth!
+Instead, I would argue that this field of research provides the closest approximation to realistic visualizations that desktop hardware can currently support.
+Many art and video game studios are interested in telling a complete story via computational media, and this simply would not be possible without the rigorous efforts of researchers from around the world.
+This is why Pixar hires researchers and will actively publish their findings after their movies are released.
+
+Though the boundary between computer science research fields is a bit vague, for the purposes of the Algorithm Archive, we will broadly classify computer graphics as anything with direct applications to images or fields that can be represented as images.
+Convolutions, for example, would not be considered part of computer graphics because they are used widely in all areas of computer science research; however, Canny edge detection will be.
+We will also be covering a wide range of applications that are used for rendering high-resolution graphics and computational art.
+
+As with all sections to the Algorithm Archive, this is a work in progress and subject to change, so feel free to let me know what you think!

contents/flood_fill/code/julia/flood_fill.jl

@@ -0,0 +1,153 @@
+using DataStructures
+using Test
+
+# Function to check to make sure we are on the canvas
+function inbounds(canvas_size, loc)
+
+    # Make sure we are not beneath or to the left of the canvas
+    if minimum(Tuple(loc)) < 1
+        return false
+
+    # Make sure we are not to the right of the canvas
+    elseif loc[2] > canvas_size[2]
+        return false
+
+    # Make sure we are not above the canvas
+    elseif loc[1] > canvas_size[1]
+        return false
+    else
+        return true
+    end
+end
+
+function color!(canvas, loc::CartesianIndex, old_val, new_val)
+    # bounds check, do not color if no in bounds!
+    if !inbounds(size(canvas), loc)
+        return
+    end
+
+    # Only change color if the element value is the old value
+    if (canvas[loc] != old_val)
+        return
+    else
+        canvas[loc] = new_val
+    end
+end
+
+function find_neighbors(canvas, loc::CartesianIndex, old_val, new_val)
+    
+    # Finding north, south, east, west neighbors
+    possible_neighbors = [loc + CartesianIndex(0, 1),
+                          loc + CartesianIndex(1, 0),
+                          loc + CartesianIndex(0, -1),
+                          loc + CartesianIndex(-1, 0)]
+
+    # Exclusing neighbors that should not be colored
+    neighbors =  []
+    for possible_neighbor in possible_neighbors
+        if inbounds(size(canvas), possible_neighbor) &&
+           canvas[possible_neighbor] == old_val
+            push!(neighbors, possible_neighbor)
+        end
+    end
+
+    return neighbors
+end
+
+function stack_fill!(canvas, loc::CartesianIndex, old_val, new_val)
+    if new_val == old_val
+        return
+    end
+
+    s = Stack{CartesianIndex}()
+    push!(s, loc)
+
+    while length(s) > 0
+        current_loc = pop!(s)
+        if canvas[current_loc] == old_val
+            color!(canvas, current_loc, old_val, new_val)
+            possible_neighbors = find_neighbors(canvas, current_loc,
+                                                old_val, new_val)
+            for neighbor in possible_neighbors
+                push!(s,neighbor)
+            end
+        end
+        
+    end
+end
+
+
+function queue_fill!(canvas, loc::CartesianIndex, old_val, new_val)
+    if new_val == old_val
+        return
+    end
+
+    q = Queue{CartesianIndex}()
+    enqueue!(q, loc)
+
+    # Coloring the initial location
+    color!(canvas, loc, old_val, new_val)
+
+    while length(q) > 0
+        current_loc = dequeue!(q)
+
+        possible_neighbors = find_neighbors(canvas, current_loc,
+                                            old_val, new_val)
+
+        # Coloring as we are enqueuing neighbors
+        for neighbor in possible_neighbors
+            color!(canvas, neighbor, old_val, new_val)
+            enqueue!(q,neighbor)
+        end
+        
+    end
+end
+
+function recursive_fill!(canvas, loc::CartesianIndex, old_val, new_val)
+
+    if (old_val == new_val)
+        return
+    end
+
+    color!(canvas, loc, old_val, new_val)
+
+    possible_neighbors = find_neighbors(canvas, loc, old_val, new_val)
+    for possible_neighbor in possible_neighbors
+        recursive_fill!(canvas, possible_neighbor, old_val, new_val)
+    end
+end
+
+function main()
+
+    # Creation of a 5x5 grid with a single row of 1.0 elements 
+    grid = zeros(5,5)
+    grid[3,:] .= 1
+
+    # Create solution grid
+    answer_grid = zeros(5,5)
+    answer_grid[1:3, :] .= 1
+
+    # Start filling at 1,1
+    start_loc = CartesianIndex(1,1)
+
+    @testset "Fill Methods" begin
+        # Use recursive method and reinitialize grid
+        recursive_fill!(grid, start_loc, 0.0, 1.0)
+        @test grid == answer_grid
+
+        grid[1:2,:] .= 0
+
+        # Use queue method and reinitialize grid
+        queue_fill!(grid, start_loc, 0.0, 1.0)
+        @test grid == answer_grid
+
+        grid[1:2,:] .= 0
+
+        # Use stack method and reinitialize grid
+        stack_fill!(grid, start_loc, 0.0, 1.0)
+        @test grid == answer_grid
+    end
+
+end
+
+main()