From 2129316819f9e9ea2c849f8d3001cf452c51fe4d Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Sat, 22 Jun 2019 11:20:24 +0200
Subject: Extract parameters in GL interop example

---
 ldc_2d_gl_interop.py | 59 +++++++++++++++++++++++++++++++++++++---------------
 1 file changed, 42 insertions(+), 17 deletions(-)

diff --git a/ldc_2d_gl_interop.py b/ldc_2d_gl_interop.py
index a10664d..26a8dea 100644
--- a/ldc_2d_gl_interop.py
+++ b/ldc_2d_gl_interop.py
@@ -14,6 +14,11 @@ from OpenGL.GL import shaders
 
 screen_x = 1920
 screen_y = 1200
+cells_per_pixel   = 4
+updates_per_frame = 200
+
+lid_speed = 0.1
+relaxation_time = 0.515
 
 def cavity(geometry, x, y):
     if x == 1 or y == 1 or x == geometry.size_x-2:
@@ -23,19 +28,21 @@ def cavity(geometry, x, y):
     else:
         return 1
 
-boundary = """
+boundary = Template("""
     if ( m == 2 ) {
         u_0 = 0.0;
         u_1 = 0.0;
     }
     if ( m == 3 ) {
-        u_0 = 0.1;
+        u_0 = $lid_speed;
         u_1 = 0.0;
     }
-"""
+""").substitute({
+    'lid_speed': lid_speed
+})
 
 def get_projection():
-    scale = numpy.diag([8.0/screen_x, 8.0/screen_y, 1.0, 1.0])
+    scale = numpy.diag([(2.0*cells_per_pixel)/screen_x, (2.0*cells_per_pixel)/screen_y, 1.0, 1.0])
     translation        = numpy.matrix(numpy.identity(4))
     translation[3,0:3] = [-1.0, -1.0, 0.0]
     return scale * translation;
@@ -62,43 +69,60 @@ vertex_shader = shaders.compileShader(Template("""
 
 layout (location=0) in vec4 CellMoments;
 
+out vec3 color;
+
 uniform mat4 projection;
 
+vec3 blueRedPalette(float x) {
+    return mix(
+        vec3(0.0, 0.0, 1.0),
+        vec3(1.0, 0.0, 0.0),
+        x
+    );
+}
+
 vec2 fluidVertexAtIndex(uint i) {
     const float y = floor(float(i) / $size_x);
-	return vec2(
-		i - $size_x*y,
-		y
-	);
+    return vec2(
+        i - $size_x*y,
+        y
+    );
 }
 
 void main() {
     const vec2 idx = fluidVertexAtIndex(gl_VertexID);
 
     gl_Position = projection * vec4(
-        idx.x + 500.*CellMoments[1],
-        idx.y + 500.*CellMoments[2],
+        idx.x,
+        idx.y,
         0.,
         1.
     );
-}""").substitute({'size_x': screen_x//4}), GL_VERTEX_SHADER)
+
+    color = blueRedPalette(CellMoments[3] / $lid_speed);
+}""").substitute({
+    'size_x'   : screen_x//cells_per_pixel,
+    'lid_speed': lid_speed
+}), GL_VERTEX_SHADER)
 
 fragment_shader = shaders.compileShader("""
-#version 120
+#version 430
+
+in vec3 color;
+
 void main(){
-    gl_FragColor = vec4(1,1,1,1);
+	gl_FragColor = vec4(color.xyz, 0.0);
 }""", GL_FRAGMENT_SHADER)
 
 
-
 shader_program = shaders.compileProgram(vertex_shader, fragment_shader)
 projection_id = shaders.glGetUniformLocation(shader_program, 'projection')
 
 lattice = Lattice(
     descriptor   = D2Q9,
-    geometry     = Geometry(screen_x//4, screen_y//4),
+    geometry     = Geometry(screen_x//cells_per_pixel, screen_y//cells_per_pixel),
     moments      = lbm.moments(optimize = True),
-    collide      = lbm.bgk(f_eq = lbm.equilibrium(), tau = 0.515),
+    collide      = lbm.bgk(f_eq = lbm.equilibrium(), tau = relaxation_time),
     boundary_src = boundary,
     opengl       = True
 )
@@ -108,7 +132,7 @@ lattice.setup_geometry(cavity)
 projection = get_projection()
 
 def on_display():
-    for i in range(0,60):
+    for i in range(0,updates_per_frame):
         lattice.evolve()
 
     lattice.sync_gl_moments()
@@ -123,6 +147,7 @@ def on_display():
 
     glVertexPointer(4, GL_FLOAT, 0, lattice.gl_moments)
 
+    glPointSize(cells_per_pixel)
     glDrawArrays(GL_POINTS, 0, lattice.geometry.volume)
 
     glDisableClientState(GL_VERTEX_ARRAY)
-- 
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