Simple (but insanly fast compared to CPU) fragment shader to draw mandelbrot set

2 files changed, 40 insertions, 2 deletions

diff --git a/shader/fragment.glsl b/shader/fragment.glsl
index 3fbeac5..19b020e 100644
--- a/shader/fragment.glsl
+++ b/shader/fragment.glsl
@@ -1,8 +1,43 @@
 #version 400 core
 
-out vec4 out_color;
+out vec4        out_color;
+
+uniform int     u_width;
+uniform int     u_height;
+
+uniform float   u_real_start;
+uniform float   u_real_end;
+uniform float   u_imag_start;
+uniform float   u_imag_end;
+
+uniform int     u_iterations;
 
 void main()
 {
-    out_color = vec4(1.0, 1.0, 1.0, 1.0);
+    float   ca = u_real_start + float(gl_FragCoord.x) / float(u_width) * (u_real_end - u_real_start);
+    float   cb = u_imag_start + float(gl_FragCoord.y) / float(u_height) * (u_imag_end - u_imag_start);
+    float	zr = ca;
+    float	zi = cb;
+    float	zr_square;
+    float	zi_square;
+    int		n;
+
+    for (n = 0; n < u_iterations; n++)
+    {
+        zi_square = zi * zi;
+        zr_square = zr * zr;
+        if (zr_square + zi_square > 4.0)
+            break;
+        zi = 2.0 * zr * zi;
+        zr = zr_square - zi_square;
+        zi += cb;
+        zr += ca;
+    }
+
+    out_color = vec4(
+        float(n) / float(u_iterations),
+        float(n) / float(u_iterations),
+        0.0,
+        1.0
+    );
 }
diff --git a/shader/vertex.glsl b/shader/vertex.glsl
index 9ec6439..714e089 100644
--- a/shader/vertex.glsl
+++ b/shader/vertex.glsl
@@ -1,5 +1,8 @@
 #version 400 core
 
+layout (location = 0) in vec2 in_position;
+
 void main()
 {
+    gl_Position = vec4(in_position, 0.0, 1.0);
 }