tutorial: HLSL version of the graph plotting shader.

tutorial/04_texture.lolfx

@@ -74,3 +74,71 @@ void main(void)
     gl_FragColor = vec4(mix(p.x, 1.0, lum), lum, lum, 1.0);
 }
 
+[vert.hlsl]
+
+void main(float2 in_Position : POSITION,
+          out float4 out_Position : POSITION,
+          out float4 pass_Position : TEXCOORD0)
+{
+    pass_Position = float4(0.5 * in_Position + 0.5, 0.0, 1.0);
+    out_Position = float4(in_Position, 0.5, 1.0);
+}
+
+[frag.hlsl]
+
+float segdist(float2 p1, float2 p2, float2 a)
+{
+    float d = max(1e-10, dot(p2 - p1, p2 - p1));
+    float t = clamp(dot(a - p1, p2 - p1) / d, 0.0, 1.0);
+    return distance(a, lerp(p1, p2, t));
+}
+
+void main(in float4 pass_Position : TEXCOORD0,
+          uniform sampler2D u_Texture,
+          out float4 out_FragColor : COLOR)
+{
+    float width = 800.0;
+    float height = 600.0;
+    float texture_width = 256.0;
+    float line_width = 1.2;
+    float dot_size = 1.0;
+    float4 delta = float4(1.0 / texture_width, 0.0,
+                          2.0 / texture_width, 0.0);
+
+    float2 p = pass_Position.xy;
+    float2 tc = float2(floor(p.x * texture_width) / texture_width, p.y);
+    float t = p.x * texture_width - floor(p.x * texture_width);
+    float4 c;
+    c[0] = tex2D(u_Texture, tc - delta.xy).x;
+    c[1] = tex2D(u_Texture, tc).x;
+    c[2] = tex2D(u_Texture, tc + delta.xy).x;
+    c[3] = tex2D(u_Texture, tc + delta.zw).x;
+
+    /* Find the 4 closest points in screen space */
+    float2 p0 = float2((tc.x - delta.x) * width, c[0] * height);
+    float2 p1 = float2((tc.x          ) * width, c[1] * height);
+    float2 p2 = float2((tc.x + delta.x) * width, c[2] * height);
+    float2 p3 = float2((tc.x + delta.z) * width, c[3] * height);
+    float2 a = float2(p.x * width, p.y * height);
+
+    /* Compute distance to segments */
+    float d =        segdist(p0, p1, a);
+          d = min(d, segdist(p1, p2, a));
+          d = min(d, segdist(p2, p3, a));
+
+    /* Compute distance to dots */
+    d = min(d, length(a - p0) - dot_size);
+    d = min(d, length(a - p1) - dot_size);
+    d = min(d, length(a - p2) - dot_size);
+    d = min(d, length(a - p3) - dot_size);
+
+    /* Add line width */
+    float lum = clamp(line_width - d, 0.0, 1.0);
+
+    /* Compensate for sRGB */
+    lum = pow(1.0 - lum, 1.0 / 2.4);
+
+    /* Choose some funny colours */
+    out_FragColor = float4(lerp(p.x, 1.0, lum), lum, lum, 1.0);
+}
+