From 26e09c9f01eaf997b0b4f8fa831ed3873f66465a Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Sat, 28 Mar 2020 19:55:14 +0100
Subject: Draw spheres in correct size

…using billboarding.
---
 boltzgas/visual/shader.py | 15 ++++++++-
 boltzgas/visual/view.py   | 78 ++++++++++++++++++++++++++++++++++++-----------
 2 files changed, 74 insertions(+), 19 deletions(-)

diff --git a/boltzgas/visual/shader.py b/boltzgas/visual/shader.py
index b4295a8..c6c035b 100644
--- a/boltzgas/visual/shader.py
+++ b/boltzgas/visual/shader.py
@@ -1,4 +1,4 @@
-from OpenGL.GL import GL_VERTEX_SHADER, GL_FRAGMENT_SHADER
+from OpenGL.GL import GL_VERTEX_SHADER, GL_FRAGMENT_SHADER, GL_GEOMETRY_SHADER
 from OpenGL.GL import shaders
 
 class Shader:
@@ -13,3 +13,16 @@ class Shader:
     def use(self):
         shaders.glUseProgram(self.program)
 
+class GeometryShader:
+    def __init__(self, fragment_src, geometry_src, vertex_src, uniform):
+        self.program = shaders.compileProgram(
+            shaders.compileShader(vertex_src, GL_VERTEX_SHADER),
+            shaders.compileShader(geometry_src, GL_GEOMETRY_SHADER),
+            shaders.compileShader(fragment_src, GL_FRAGMENT_SHADER))
+        self.uniform = { }
+        for name in uniform:
+            self.uniform[name] = shaders.glGetUniformLocation(self.program, name)
+
+    def use(self):
+        shaders.glUseProgram(self.program)
+
diff --git a/boltzgas/visual/view.py b/boltzgas/visual/view.py
index bdc18e8..7d7d2cc 100644
--- a/boltzgas/visual/view.py
+++ b/boltzgas/visual/view.py
@@ -5,7 +5,7 @@ from pyrr import matrix44
 
 import numpy as np
 
-from .shader import Shader
+from .shader import Shader, GeometryShader
 from .camera import Projection, Rotation, MouseDragMonitor, MouseScrollMonitor
 
 particle_shader = (
@@ -16,43 +16,86 @@ particle_shader = (
 
         uniform vec4 camera_pos;
 
+        in GS_OUT
+        {
+            vec3 particle_pos;
+            vec2 tex_coord;
+        } fs_in;
+
         void main(){
-            if (length(gl_PointCoord - vec2(0.5)) > 0.5) {
+            if (length(fs_in.tex_coord - vec2(0.5)) > 0.5) {
                 discard;
             }
 
-            vec3 n = vec3(gl_PointCoord - vec2(0.5), 0.);
+            vec3 n = vec3(fs_in.tex_coord - vec2(0.5), 0.);
             n.z = -sqrt(1.0 - length(n));
             n = normalize(n);
 
-            vec3 dir = normalize(camera_pos.xyz - particle_pos);
-            vec3 color = vec3(1.) * dot(dir, n);
+            vec3 dir = normalize(camera_pos.xyz - fs_in.particle_pos);
+            vec3 color = vec3(1.) * max(0., dot(dir, n));
 
-            gl_FragColor = vec4(max(vec3(0.5), color.xyz), 1.0);
+            gl_FragColor = vec4(color.xyz, 1.0);
         }
     """,
     """
         #version 430
 
-        layout (location=0) in vec4 particles;
+        layout (points) in;
+        layout (triangle_strip, max_vertices=4) out;
 
-        out vec3 color;
-        out vec3 particle_pos;
+        out GS_OUT
+        {
+            vec3 particle_pos;
+            vec2 tex_coord;
+        } gs_out;
 
         uniform mat4 projection;
         uniform mat4 rotation;
 
-        uniform vec3 face_color;
-        uniform vec3 trace_color;
-        uniform uint trace_id;
         uniform vec4 camera_pos;
 
+        uniform float radius;
+
+        vec4 project(vec3 v) {
+            return projection * rotation * vec4(v, 1.);
+        }
+
+        void emitSquareAt(vec3 position) {
+            mat4 m = projection * rotation;
+            vec3 camera_right = normalize(vec3(m[0][0], m[1][0], m[2][0]));
+            vec3 camera_up = normalize(vec3(m[0][1], m[1][1], m[2][1]));
+
+            gs_out.particle_pos = gl_in[0].gl_Position.xyz;
+
+            gl_Position = project(position + camera_right * -radius + camera_up * -radius);
+            gs_out.tex_coord = vec2(0.,0.);
+            EmitVertex();
+            gl_Position = project(position + camera_right *  radius + camera_up * -radius);
+            gs_out.tex_coord = vec2(1.,0.);
+            EmitVertex();
+            gl_Position = project(position + camera_right * -radius + camera_up *  radius);
+            gs_out.tex_coord = vec2(0.,1.);
+            EmitVertex();
+            gl_Position = project(position + camera_right *  radius + camera_up *  radius);
+            gs_out.tex_coord = vec2(1.,1.);
+            EmitVertex();
+        }
+
+        void main() {
+            emitSquareAt(gl_in[0].gl_Position.xyz);
+            EndPrimitive();
+        }
+    """,
+    """
+        #version 430
+
+        layout (location=0) in vec4 particle_pos;
+
         void main() {
-            gl_Position = projection * rotation * vec4(particles.xyz, 1.);
-            particle_pos = gl_Position.xyz;
+            gl_Position = vec4(particle_pos.xyz, 1.0);
         }
     """,
-    ['projection', 'rotation', 'camera_pos']
+    ['projection', 'rotation', 'camera_pos', 'radius']
 )
 
 decoration_shader = (
@@ -122,7 +165,7 @@ class View:
         self.instruments = instruments
 
         self.texture_shader    = Shader(*texture_shader)
-        self.particle_shader   = Shader(*particle_shader)
+        self.particle_shader   = GeometryShader(*particle_shader)
         self.decoration_shader = Shader(*decoration_shader)
 
         self.camera_projection = Projection(distance = 5)
@@ -169,9 +212,8 @@ class View:
         glUniformMatrix4fv(self.particle_shader.uniform['projection'], 1, False, np.ascontiguousarray(self.camera_projection.get()))
         glUniformMatrix4fv(self.particle_shader.uniform['rotation'],   1, False, np.ascontiguousarray(self.camera_rotation.get()))
         glUniform4fv(self.particle_shader.uniform['camera_pos'], 1, self.camera_pos)
+        glUniform1f(self.particle_shader.uniform['radius'], self.gas.radius)
 
-        glEnable(GL_POINT_SPRITE)
-        glPointSize(2*self.gas.radius*self.pixels_per_unit)
         self.gas.gl_draw_particles()
         glBindVertexArray(0)
 
-- 
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