polyvox/examples/common/PolyVoxExample.h

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Copyright (c) 2015 David Williams and Matthew Williams

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#ifndef __PolyVoxExample_H__
#define __PolyVoxExample_H__

#include "OpenGLWidget.h"

#include "PolyVox/Mesh.h"

#include <QGLShaderProgram>
#include <QOpenGLBuffer>
#include <QOpenGLFunctions_3_1>
#include <QOpenGLVertexArrayObject>

// This structure holds all the data required
// to render one of our meshes through OpenGL. 
struct OpenGLMeshData
{
	GLuint noOfIndices;
	GLenum indexType;
	GLuint indexBuffer;
	GLuint vertexBuffer;
	GLuint vertexArrayObject;
	QVector3D translation;
	float scale;
};

class PolyVoxExample : public OpenGLWidget<QOpenGLFunctions_3_1>
{
public:
	PolyVoxExample(QWidget *parent)
		:OpenGLWidget(parent)
	{
	}

	// For our purposes we use a single shader for the whole volume, and
	// this example framework is only meant to show a single volume at a time
	void setShader(QSharedPointer<QGLShaderProgram> shader);

	// Convert a PolyVox mesh to OpenGL index/vertex buffers. Inlined because it's templatised.
	template <typename MeshType>
	void addMesh(const MeshType& surfaceMesh, const PolyVox::Vector3DInt32& translation = PolyVox::Vector3DInt32(0, 0, 0), float scale = 1.0f)
	{
		// Convienient access to the vertices and indices
		const auto& vecIndices = surfaceMesh.getIndices();
		const auto& vecVertices = surfaceMesh.getVertices();

		// This struct holds the OpenGL properties (buffer handles, etc) which will be used
		// to render our mesh. We copy the data from the PolyVox mesh into this structure.
		OpenGLMeshData meshData;

		// Create the VAO for the mesh
		glGenVertexArrays(1, &(meshData.vertexArrayObject));
		glBindVertexArray(meshData.vertexArrayObject);

		// The GL_ARRAY_BUFFER will contain the list of vertex positions
		glGenBuffers(1, &(meshData.vertexBuffer));
		glBindBuffer(GL_ARRAY_BUFFER, meshData.vertexBuffer);
		glBufferData(GL_ARRAY_BUFFER, vecVertices.size() * sizeof(typename MeshType::VertexType), vecVertices.data(), GL_STATIC_DRAW);

		// and GL_ELEMENT_ARRAY_BUFFER will contain the indices
		glGenBuffers(1, &(meshData.indexBuffer));
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, meshData.indexBuffer);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, vecIndices.size() * sizeof(typename MeshType::IndexType), vecIndices.data(), GL_STATIC_DRAW);

		// Every surface extractor outputs valid positions for the vertices, so tell OpenGL how these are laid out
		glEnableVertexAttribArray(0); // Attrib '0' is the vertex positions
		glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(typename MeshType::VertexType), (GLvoid*)(offsetof(typename MeshType::VertexType, position))); //take the first 3 floats from every sizeof(decltype(vecVertices)::value_type)

		// Some surface extractors also generate normals, so tell OpenGL how these are laid out. If a surface extractor
		// does not generate normals then nonsense values are written into the buffer here and sghould be ignored by the
		// shader. This is mostly just to simplify this example code - in a real application you will know whether your
		// chosen surface extractor generates normals and can skip uploading them if not.
		glEnableVertexAttribArray(1); // Attrib '1' is the vertex normals.
		glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(typename MeshType::VertexType), (GLvoid*)(offsetof(typename MeshType::VertexType, normal)));

		// Finally a surface extractor will probably output additional data. This is highly application dependant. For this example code 
		// we're just uploading it as a set of bytes which we can read individually, but real code will want to do something specialised here.
		glEnableVertexAttribArray(2); //We're talking about shader attribute '2'
		GLint size = (std::min)(sizeof(typename MeshType::VertexType::DataType), size_t(4)); // Can't upload more that 4 components (vec4 is GLSL's biggest type)
		glVertexAttribIPointer(2, size, GL_UNSIGNED_BYTE, sizeof(typename MeshType::VertexType), (GLvoid*)(offsetof(typename MeshType::VertexType, data)));

		// We're done uploading and can now unbind.
		glBindVertexArray(0);

		// A few additional properties can be copied across for use during rendering.
		meshData.noOfIndices = vecIndices.size();
		meshData.translation = QVector3D(translation.getX(), translation.getY(), translation.getZ());
		meshData.scale = scale;

		// Set 16 or 32-bit index buffer size.
		meshData.indexType = sizeof(typename MeshType::IndexType) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT;

		// Now add the mesh to the list of meshes to render.
		addMeshData(meshData);
	}

	void addMeshData(OpenGLMeshData meshData)
	{
		mMeshData.push_back(meshData);
	}

protected:
	const float PI = 3.14159265358979f;

	virtual void initializeExample() {};

	void initialize() override
	{
		mShader = QSharedPointer<QGLShaderProgram>(new QGLShaderProgram);

		// This is basically a simple fallback vertex shader which does the most basic rendering possible.  
		// PolyVox examples are able to provide their own shaders to demonstrate certain effects if desired. 
		if (!mShader->addShaderFromSourceFile(QGLShader::Vertex, ":/example.vert"))
		{
			std::cerr << mShader->log().toStdString() << std::endl;
			exit(EXIT_FAILURE);
		}

		// This is basically a simple fallback fragment shader which does the most basic rendering possible.  
		// PolyVox examples are able to provide their own shaders to demonstrate certain effects if desired. 
		if (!mShader->addShaderFromSourceFile(QGLShader::Fragment, ":/example.frag"))
		{
			std::cerr << mShader->log().toStdString() << std::endl;
			exit(EXIT_FAILURE);
		}

		// Bind the position semantic - this is defined in the vertex shader above.
		mShader->bindAttributeLocation("position", 0);

		// Bind the other semantics. Note that these don't actually exist in our example shader above! However, other
		// example shaders may choose to provide them and having the binding code here does not seem to cause any problems.
		mShader->bindAttributeLocation("normal", 1);
		mShader->bindAttributeLocation("material", 2);

		if (!mShader->link())
		{
			std::cerr << mShader->log().toStdString() << std::endl;
			exit(EXIT_FAILURE);
		}

		// Now do any initialization for the specific example.
		initializeExample();
	}

	void renderOneFrame() override
	{
		// Our example framework only uses a single shader for the scene (for all meshes).
		mShader->bind();

		// These two matrices are constant for all meshes.
		mShader->setUniformValue("viewMatrix", viewMatrix());
		mShader->setUniformValue("projectionMatrix", projectionMatrix());

		// Iterate over each mesh which the user added to our list, and render it.
		for (OpenGLMeshData meshData : mMeshData)
		{
			//Set up the model matrrix based on provided translation and scale.
			QMatrix4x4 modelMatrix;
			modelMatrix.translate(meshData.translation);
			modelMatrix.scale(meshData.scale);
			mShader->setUniformValue("modelMatrix", modelMatrix);

			// Bind the vertex array for the current mesh
			glBindVertexArray(meshData.vertexArrayObject);
			// Draw the mesh
			glDrawElements(GL_TRIANGLES, meshData.noOfIndices, meshData.indexType, 0);
			// Unbind the vertex array.
			glBindVertexArray(0);
		}

		// We're done with the shader for this frame.
		mShader->release();
	}

private:
	// Index/vertex buffer data
	std::vector<OpenGLMeshData> mMeshData;

	QSharedPointer<QGLShaderProgram> mShader;
};

#endif //__PolyVoxExample_H__