Line Stipple Shader

src/material.cpp

@@ -62,6 +62,10 @@ RenderableMaterial::RenderableMaterial(Qt3DCore::QNode *parent, VertexShaderType
             shader3->setGeometryShaderCode(
                 Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/shaders/shaders/line_tesselator.geom"))));
             break;
+        case (GeometryShaderType::LineStipple):
+            shader3->setGeometryShaderCode(
+                Qt3DRender::QShaderProgram::loadSource(QUrl(QStringLiteral("qrc:/shaders/shaders/line_stipple.geom"))));
+            break;
         default:
             throw(std::runtime_error("Unhandled geometry shader type.\n"));
     }
@@ -122,4 +126,4 @@ void RenderableMaterial::setSpecular(QColor specular)
 {
     specular_ = specular;
     specularParameter_->setValue(specular_);
-}
+}

src/material.h

@@ -19,7 +19,8 @@ class RenderableMaterial : public Qt3DRender::QMaterial
     enum class GeometryShaderType
     {
         None,
-        LineTesselator
+        LineTesselator,
+        LineStipple
     };
     // Fragment Shader Types
     enum class FragmentShaderType
@@ -56,4 +57,4 @@ class RenderableMaterial : public Qt3DRender::QMaterial
     // Set specular colour component
     void setSpecular(QColor specular);
 };
-} // namespace Mildred
+} // namespace Mildred

src/shaders.qrc

@@ -6,5 +6,6 @@
     <file>shaders/phongpervertex.frag</file>
     <file>shaders/monochrome.frag</file>
     <file>shaders/line_tesselator.geom</file>
+    <file>shaders/line_stipple.geom</file>
   </qresource>
 </RCC>

src/shaders/line_stipple.geom

@@ -0,0 +1,79 @@
+#version 330
+
+layout(lines) in;
+layout(triangle_strip, max_vertices = 4) out;
+
+// Input Vertex Data
+in worldData
+{
+    vec3 position;
+    vec3 normal;
+    vec4 color;
+}
+vertices[];
+
+// Output Fragment Data
+out fragData
+{
+    vec3 position;
+    vec3 normal;
+    vec4 color;
+}
+frag;
+
+uniform vec2 viewportSize;
+uniform float lineWidth = 1.5;
+
+// Copy clip distances for specified input vertex
+void applyClipping(int inVertexID)
+{
+    gl_ClipDistance[0] = gl_in[inVertexID].gl_ClipDistance[0];
+    gl_ClipDistance[1] = gl_in[inVertexID].gl_ClipDistance[1];
+    gl_ClipDistance[2] = gl_in[inVertexID].gl_ClipDistance[2];
+    gl_ClipDistance[3] = gl_in[inVertexID].gl_ClipDistance[3];
+    gl_ClipDistance[4] = gl_in[inVertexID].gl_ClipDistance[4];
+    gl_ClipDistance[5] = gl_in[inVertexID].gl_ClipDistance[5];
+}
+
+void main()
+{
+    vec4 p1 = gl_in[0].gl_Position;
+    vec4 p2 = gl_in[1].gl_Position;
+
+    vec2 dir = normalize((p2.xy - p1.xy) * viewportSize);
+    vec2 offset = vec2(-dir.y, dir.x) * lineWidth / viewportSize;
+
+    // Emit the four corners of our two triangles
+    gl_Position = p1 + vec4(offset.xy * p1.w, 0.0, 0.0);
+    applyClipping(0);
+    frag.position = vec3(gl_Position);
+    frag.color = vertices[0].color;
+    frag.normal = vertices[1].normal;
+    EmitVertex();
+    gl_Position = p1 - vec4(offset.xy * p1.w, 0.0, 0.0);
+    applyClipping(0);
+    frag.position = vec3(gl_Position);
+    frag.color = vertices[0].color;
+    frag.normal = vertices[0].normal;
+    EmitVertex();
+    gl_Position = p2 + vec4(offset.xy * p2.w, 0.0, 0.0);
+    applyClipping(1);
+    frag.position = vec3(gl_Position);
+    frag.color = vertices[1].color;
+    frag.normal = vertices[1].normal;
+    EmitVertex();
+    gl_Position = p2 - vec4(offset.xy * p2.w, 0.0, 0.0);
+    applyClipping(1);
+    frag.position = vec3(gl_Position);
+    frag.color = vertices[1].color;
+    frag.normal = vertices[1].normal;
+
+    // To view line-stipple output, remove comment bars (//) from the following two lines
+    //gl_Position = p1 + vec4(offset.xy * p1.w, 0.0, 0.0);
+    //applyClipping(0);
+
+    EmitVertex();
+
+    EndPrimitive();
+
+}

src/widget.cpp

@@ -195,7 +195,7 @@ Data1DEntity *MildredWidget::addData1D(std::string_view tag)
 
     // Add a material
     auto *material = createMaterial(entity, RenderableMaterial::VertexShaderType::ClippedToDataVolume,
-                                    RenderableMaterial::GeometryShaderType::LineTesselator,
+                                    RenderableMaterial::GeometryShaderType::LineStipple,
                                     RenderableMaterial::FragmentShaderType::PerVertexPhong);
     entity->setDataMaterial(material);
     entity->setErrorMaterial(material);
@@ -214,4 +214,4 @@ DisplayGroup *MildredWidget::addDisplayGroup()
     auto newGroup = displayGroups_.emplace_back(std::make_shared<DisplayGroup>());
 
     return newGroup.get();
-}
+}