tutorial: change the terrain drawing into an antialiased line graph.

tutorial/04_texture.cpp

@@ -1,5 +1,5 @@
 //
-// Lol Engine - Noise tutorial
+// Lol Engine - Graphing tutorial
 //
 // Copyright: (c) 2012 Sam Hocevar <sam@hocevar.net>
 //   This program is free software; you can redistribute it and/or
@@ -18,6 +18,8 @@
 using namespace std;
 using namespace lol;
 
+static int const TEXTURE_WIDTH = 128;
+
 extern char const *lolfx_04_texture;
 
 class TextureDemo : public WorldEntity
@@ -34,7 +36,7 @@ public:
         m_vertices << vec2( 1.0, -1.0);
         m_vertices << vec2( 1.0,  1.0);
 
-        m_heightmap = new uint8_t[4 * 512 * 1];
+        m_heightmap = new uint8_t[4 * TEXTURE_WIDTH * 1];
     }
 
     virtual ~TextureDemo()
@@ -46,45 +48,18 @@ public:
     {
         WorldEntity::TickGame(seconds);
 
-        /* Generate a new heightmap every 400 frames */
-        if (m_frames % 400 == 0)
-        {
-            for (int i = 0, height = 64; i < 512; i++)
-            {
-                m_heightmap[4 * i] = height;
-                m_heightmap[4 * i + 1] = 255; /* unused */
-                m_heightmap[4 * i + 2] = 255; /* unused */
-                m_heightmap[4 * i + 3] = 255; /* unused */
-    
-                height += rand() % 17 - 8;
-                height += rand() % 17 - 8;
-                height = std::max(15, std::min(height, 240));
-            }
-        }
+        /* Generate a new heightmap at the beginning */
+        if (m_frames == 0)
+            memset(m_heightmap, 255, 4 * TEXTURE_WIDTH);
 
-        /* Slightly disturb the terrain */
-        for (int i = 1; i < 511; i++)
-        {
-            int delta = (rand() & 1) ? 1 : -1;
-
-            if (rand() & 3)
-                continue;
-
-            uint8_t &center = m_heightmap[4 * i];
-            uint8_t &side1 = m_heightmap[4 * (i - delta)];
-            uint8_t &side2 = m_heightmap[4 * (i + delta)];
-
-            if (center > side1)
-            {
-                center--;
-                side1++;
-            }
-            else if (center > side2)
-            {
-                center--;
-                side2++;
-            }
-        }
+        /* Scroll left */
+        for (int i = 0; i < TEXTURE_WIDTH - 1; i++)
+            m_heightmap[4 * i] = m_heightmap[4 * i + 4];
+
+        int height = m_heightmap[4 * (TEXTURE_WIDTH - 1)];
+        height = height / 2 + 255 / 4 + rand() % 97 - 48;
+        height = std::max(15, std::min(height, 240));
+        m_heightmap[4 * (TEXTURE_WIDTH - 1)] = height;
 
         /* Update frame counter */
         ++m_frames;
@@ -97,7 +72,7 @@ public:
         /* Initialise GPU data */
         if (!m_ready)
         {
-            m_texture = new Texture(ivec2(512, 1), PixelFormat::A8R8G8B8);
+            m_texture = new Texture(ivec2(TEXTURE_WIDTH, 1), PixelFormat::A8R8G8B8);
 
             m_shader = Shader::Create(lolfx_04_texture);
             m_coord = m_shader->GetAttribLocation("in_Position", VertexUsage::Position, 0);

tutorial/04_texture.lolfx

@@ -25,40 +25,56 @@ float rand(in vec2 p, in float v)
     return fract(v * sin(dot(p, vec2(1298.9837, 7823.33145))));
 }
 
+float point2segment(vec2 p1, vec2 p2, vec2 a)
+{
+    float l2 = dot(p2 - p1, p2 - p1);
+    if (l2 == 0.0)
+        return distance(a, p1);
+    float t = dot(a - p1, p2 - p1) / l2;
+    if (t < 0.0)
+        return distance(a, p1);
+    else if (t > 1.0)
+        return distance(a, p2);
+    vec2 proj = p1 + t * (p2 - p1);
+    return distance(a, proj);
+}
+
+
 void main(void)
 {
+    float width = 800.0;
+    float height = 600.0;
+    float line_width = 2.0;
+
     vec2 t = pass_Position.xy;
-    vec4 c0 = texture2D(u_Texture, t);
-    float f = rand(pass_Position.xy, 12345.67);
-
-    if (t.y > c0.x)
-    {
-        /* Sky */
-        float val = min(t.y * 2.0, 1.0);
-        if (f > 0.999)
-            gl_FragColor = vec4(1.0);
-        else
-            gl_FragColor = vec4(0.4, t.y, val, 1.0);
-    }
-    else if (t.y > c0.x - 0.03)
-    {
-        /* Grass */
-        if (f > 0.99)
-            gl_FragColor = vec4(0.4, 0.7, 0.3, 1.0);
-        else if (f > 0.9)
-            gl_FragColor = vec4(0.3, 0.6, 0.2, 1.0);
-        else
-            gl_FragColor = vec4(0.2, 0.5, 0.1, 1.0);
-    }
-    else
-    {
-        /* Earth */
-        if (f > 0.99)
-            gl_FragColor = vec4(0.7, 0.4, 0.3, 1.0);
-        else if (f > 0.9)
-            gl_FragColor = vec4(0.6, 0.3, 0.2, 1.0);
-        else
-            gl_FragColor = vec4(0.5, 0.2, 0.1, 1.0);
-    }
+    vec2 tc1 = floor(t * 128.0) / 128.0;
+    vec2 tc2 = tc1 + vec2(1.0, 1.0) / 128.0;
+    vec2 tc0 = tc1 - vec2(1.0, 1.0) / 128.0;
+    vec2 tc3 = tc2 + vec2(1.0, 1.0) / 128.0;
+
+    float c0 = texture2D(u_Texture, tc0).x;
+    float c1 = texture2D(u_Texture, tc1).x;
+    float c2 = texture2D(u_Texture, tc2).x;
+    float c3 = texture2D(u_Texture, tc3).x;
+
+    /* Artificially compress in Y */
+    c0 *= 0.3;
+    c1 *= 0.3;
+    c2 *= 0.3;
+    c3 *= 0.3;
+
+    vec2 p0 = vec2(tc0.x * width, c0 * height);
+    vec2 p1 = vec2(tc1.x * width, c1 * height);
+    vec2 p2 = vec2(tc2.x * width, c2 * height);
+    vec2 p3 = vec2(tc3.x * width, c3 * height);
+    vec2 a = vec2(t.x * width, t.y * height);
+
+    float d0 = point2segment(p0, p1, a);
+    float d1 = point2segment(p1, p2, a);
+    float d2 = point2segment(p2, p3, a);
+
+    float d = clamp(line_width - min(min(d0, d1), d2), 0.0, 1.0);
+
+    gl_FragColor = vec4(t.y, d, d * 0.3, 1.0);
 }