diff -r 0f80a2e5e42b -r 1a9eac27698d src/gl/compiler.cpp
--- a/src/gl/compiler.cpp	Fri Feb 07 02:02:16 2020 +0200
+++ b/src/gl/compiler.cpp	Fri Feb 07 23:59:06 2020 +0200
@@ -32,6 +32,7 @@
 layout(location=1) in vec4 color;
 layout(location=2) in vec3 normal;
 layout(location=3) in int id;
+layout(location=4) in int selected;
 out vec4 vColor;
 out vec3 vFragPos;
 out vec3 vNormal;
@@ -62,6 +63,10 @@
 		int b = id % 0x100;
 		vColor = vec4(r / 255.0, g / 255.0, b / 255.0, 1.0);
 	}
+	else if (selected == 1)
+	{
+		vColor = vec4(selectedColor, 1.0);
+	}
 	else
 	{
 		if (fragmentStyle == FRAGSTYLE_BfcGreen)
@@ -158,7 +163,7 @@
 			object.buffer.setUsagePattern(QOpenGLBuffer::DynamicDraw);
 			object.vertexArray.create();
 			object.vertexArray.bind();
-			for (int k : {0, 1, 2, 3})
+			for (int k : {0, 1, 2, 3, 4})
 			{
 				object.program->enableAttributeArray(k);
 			}
@@ -167,6 +172,7 @@
 			object.program->setAttributeBuffer(1, GL_FLOAT, offsetof(gl::Vertex, color), 4, stride);
 			object.program->setAttributeBuffer(2, GL_FLOAT, offsetof(gl::Vertex, normal), 3, stride);
 			glVertexAttribIPointer(3, 1, GL_INT, stride, reinterpret_cast<void*>(offsetof(gl::Vertex, id)));
+			glVertexAttribIPointer(4, 1, GL_INT, stride, reinterpret_cast<void*>(offsetof(gl::Vertex, selected)));
 			object.vertexArray.release();
 			object.buffer.release();
 			object.program->release();
@@ -189,6 +195,7 @@
 		auto& buffer = this->glObjects[arrayId].buffer;
 		auto& vector = vboData[arrayId];
 		this->storedVertexCounts[arrayId] = vector.size();
+		this->glObjects[arrayId].cachedData = vector; // todo: get rid of this copy
 		buffer.bind();
 		buffer.allocate(vector.data(), static_cast<int>(vector.size() * sizeof vector[0]));
 		buffer.release();
@@ -266,9 +273,9 @@
 	return boxCenter(this->boundingBox);
 }
 
-float gl::Compiler::modelDistance() const
+double gl::Compiler::modelDistance() const
 {
-	return longestMeasure(this->boundingBox);
+	return static_cast<double>(longestMeasure(this->boundingBox));
 }
 
 void gl::Compiler::bindVertexArray(gl::ArrayClass arrayClass)
@@ -285,6 +292,21 @@
 	object.vertexArray.release();
 }
 
+void gl::Compiler::setSelectedObjects(const QSet<ldraw::Id> ids)
+{
+	for (int i = 0; i < gl::NUM_ARRAY_CLASSES; i += 1)
+	{
+		auto& vector = this->glObjects[i].cachedData;
+		for (gl::Vertex& vertex : vector)
+		{
+			vertex.selected = (ids.contains({vertex.id})) ? 1 : 0;
+		}
+		const GLsizeiptr size = static_cast<int>(vector.size() * sizeof vector[0]);
+		this->glObjects[i].buffer.bind();
+		glBufferSubData(GL_ARRAY_BUFFER, 0, size, vector.data());
+	}
+}
+
 std::size_t gl::Compiler::vertexCount(const gl::ArrayClass arrayClass) const
 {
 	return this->storedVertexCounts[static_cast<int>(arrayClass)];