Hacky D2Q9 BGK LBM on GPU using GLSL compute shaders

Improvised on top of computicles's scaffolding.

Works in a world where _works_ is defined as "displays stuff on screen that invokes thoughts of fluid movement".

10 files changed, 364 insertions, 0 deletions

diff --git a/src/shader/code/collide.glsl b/src/shader/code/collide.glsl
new file mode 100644
index 0000000..67e762b
--- /dev/null
+++ b/src/shader/code/collide.glsl
@@ -0,0 +1,95 @@
+static const std::string COLLIDE_SHADER_CODE = R"(
+#version 430
+
+layout (local_size_x = 1, local_size_y = 1) in;
+layout (std430, binding=1) buffer bufferCollide{ float collideCells[]; };
+layout (std430, binding=2) buffer bufferStream{  float streamCells[]; };
+layout (std430, binding=3) buffer bufferFluid{   float fluidCells[]; };
+
+float get(uint x, uint y, int i, int j) {
+	return collideCells[9*128*y + 9*x + (i+1)*3 + j+1];
+}
+
+void set(uint x, uint y, int i, int j, float v) {
+	collideCells[9*128*y + 9*x + (i+1)*3 + j+1] = v;
+}
+
+void setFluid(uint x, uint y, vec2 v, float d) {
+	fluidCells[3*128*y + 3*x + 0] = float(x)-64. + 10.*v.x;
+	fluidCells[3*128*y + 3*x + 1] = float(y)-64. + 10.*v.y;
+	fluidCells[3*128*y + 3*x + 2] = d;
+}
+
+float density(uint x, uint y) {
+	return collideCells[9*128*y + 9*x + 0]
+	     + collideCells[9*128*y + 9*x + 1]
+	     + collideCells[9*128*y + 9*x + 2]
+	     + collideCells[9*128*y + 9*x + 3]
+	     + collideCells[9*128*y + 9*x + 4]
+	     + collideCells[9*128*y + 9*x + 5]
+	     + collideCells[9*128*y + 9*x + 6]
+	     + collideCells[9*128*y + 9*x + 7]
+	     + collideCells[9*128*y + 9*x + 8];
+}
+
+vec2 velocity(uint x, uint y, float d) {
+	return 1./d * vec2(
+		get(x,y, 1, 0) - get(x,y,-1, 0) + get(x,y, 1, 1) - get(x,y,-1,-1) + get(x,y, 1,-1) - get(x,y,-1,1),
+		get(x,y, 0, 1) - get(x,y, 0,-1) + get(x,y, 1, 1) - get(x,y,-1,-1) - get(x,y, 1,-1) + get(x,y,-1,1)
+	);
+}
+
+float w(int i, int j) {
+	if ( i == -1 ) {
+		if ( j != 0 ) {
+			return 1./36.;
+		} else {
+			return 1./9.;
+		}
+	} else if ( i == 0 ) {
+		if ( j != 0 ) {
+			return 1./9.;
+		} else {
+			return 4./9.;
+		}
+	} else {
+		if ( j != 0 ) {
+			return 1./36.;
+		} else {
+			return 1./9.;
+		}
+	}
+}
+
+float comp(int x, int y, vec2 v) {
+	return x*v.x + y*v.y;
+}
+
+float sq(float x) {
+	return x*x;
+}
+
+float norm(vec2 v) {
+	return sqrt(sq(v.x)+sq(v.y));
+}
+
+void main() {
+	const uint x = gl_GlobalInvocationID.x;
+	const uint y = gl_GlobalInvocationID.y;
+
+	const float omega = 0.6;
+
+	const float d = density(x,y);
+	const vec2  v = velocity(x,y,d);
+
+	setFluid(x,y,v,d);
+
+	for ( int i = -1; i <= 1; ++i ) {
+		for ( int j = -1; j <= 1; ++j ) {
+			const float eq = w(i,j) * d * (1 + 3*comp(i,j,v) + 4.5*sq(comp(i,j,v)) - 1.5*sq(norm(v)));
+			set(x,y,i,j, get(x,y,i,j) + omega * (eq - get(x,y,i,j)));
+		}
+	}
+
+}
+)";
diff --git a/src/shader/code/fragment.glsl b/src/shader/code/fragment.glsl
new file mode 100644
index 0000000..37e18bd
--- /dev/null
+++ b/src/shader/code/fragment.glsl
@@ -0,0 +1,5 @@
+static const std::string FRAGMENT_SHADER_CODE = R"(
+void main() {
+	gl_FragColor = gl_Color;
+}
+)";
diff --git a/src/shader/code/stream.glsl b/src/shader/code/stream.glsl
new file mode 100644
index 0000000..7dd5ba8
--- /dev/null
+++ b/src/shader/code/stream.glsl
@@ -0,0 +1,30 @@
+static const std::string STREAM_SHADER_CODE = R"(
+#version 430
+
+layout (local_size_x = 1, local_size_y = 1) in;
+layout (std430, binding=1) buffer bufferCollide{ float collideCells[]; };
+layout (std430, binding=2) buffer bufferStream{  float streamCells[]; };
+
+float get(uint x, uint y, int i, int j) {
+	return collideCells[9*128*y + 9*x + (i+1)*3 + j+1];
+}
+
+void set(uint x, uint y, int i, int j, float v) {
+	streamCells[9*128*y + 9*x + (i+1)*3 + j+1] = v;
+}
+
+void main() {
+	const uint x = gl_GlobalInvocationID.x;
+	const uint y = gl_GlobalInvocationID.y;
+
+	if ( x != 0 && x != 128-1 && y != 0 && y != 128-1 ) {
+		for ( int i = -1; i <= 1; ++i ) {
+			for ( int j = -1; j <= 1; ++j ) {
+				set(x+i,y+j,i,j, get(x,y,i,j));
+			}
+		}
+	} else {
+
+	}
+}
+)";
diff --git a/src/shader/code/vertex.glsl b/src/shader/code/vertex.glsl
new file mode 100644
index 0000000..4c307d8
--- /dev/null
+++ b/src/shader/code/vertex.glsl
@@ -0,0 +1,8 @@
+static const std::string VERTEX_SHADER_CODE = R"(
+uniform mat4 MVP;
+
+void main() {
+	gl_Position = MVP * vec4(gl_Vertex.xy, 0.0, 1.0);
+	gl_FrontColor = vec4(1., 0., 0., 0.);
+}
+)";
diff --git a/src/shader/util.cc b/src/shader/util.cc
new file mode 100644
index 0000000..be59ac1
--- /dev/null
+++ b/src/shader/util.cc
@@ -0,0 +1,56 @@
+#include "util.h"
+
+#include <iostream>
+#include <vector>
+
+namespace util {
+
+GLint getUniform(GLuint program, const std::string& name) {
+	const GLint uniform = glGetUniformLocation(program, name.c_str());
+
+	if ( uniform == -1 ) {
+		std::cerr << "Could not bind uniform " << name << std::endl;
+		return -1;
+	}
+
+	return uniform;
+}
+
+GLint compileShader(const std::string& source, GLenum type) {
+	GLint shader = glCreateShader(type);
+
+	if ( !shader ) {
+		std::cerr << "Cannot create a shader of type " << type << std::endl;
+		return -1;
+	}
+
+	const char* source_data = source.c_str();
+	const int source_length = source.size();
+
+	glShaderSource(shader, 1, &source_data, &source_length);
+	glCompileShader(shader);
+
+	GLint compiled;
+	glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
+
+	if ( !compiled ) {
+		std::cerr << "Cannot compile shader" << std::endl;
+
+		GLint maxLength = 0;
+		glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &maxLength);
+
+		std::vector<GLchar> errorLog(maxLength);
+		glGetShaderInfoLog(shader, maxLength, &maxLength, &errorLog[0]);
+
+		for( auto c : errorLog ) {
+			std::cerr << c;
+		}
+		std::cerr << std::endl;
+
+		return -1;
+	}
+
+	return shader;
+}
+
+}
diff --git a/src/shader/util.h b/src/shader/util.h
new file mode 100644
index 0000000..31224e9
--- /dev/null
+++ b/src/shader/util.h
@@ -0,0 +1,13 @@
+#pragma once
+
+#include <string>
+
+#include <GL/glew.h>
+
+namespace util {
+
+GLint getUniform(GLuint program, const std::string& name);
+
+GLint compileShader(const std::string& source, GLenum type);
+
+}
diff --git a/src/shader/wrap/compute_shader.cc b/src/shader/wrap/compute_shader.cc
new file mode 100644
index 0000000..c90c370
--- /dev/null
+++ b/src/shader/wrap/compute_shader.cc
@@ -0,0 +1,51 @@
+#include "compute_shader.h"
+
+#include "shader/util.h"
+
+ComputeShader::Guard::Guard(GLuint id):
+	_id(id) {
+	glUseProgram(_id);
+}
+
+ComputeShader::Guard::~Guard() {
+	glUseProgram(0);
+}
+
+ComputeShader::Guard ComputeShader::use() const {
+	return Guard(_id);
+}
+
+ComputeShader::ComputeShader(const std::string& src):
+	_id(glCreateProgram()) {
+	GLint shader = util::compileShader(src, GL_COMPUTE_SHADER);
+
+	if ( shader != -1 ) {
+		glAttachShader(_id, shader);
+		glLinkProgram(_id);
+		_good = true;
+	}
+}
+
+ComputeShader::~ComputeShader() {
+	glDeleteProgram(_id);
+}
+
+bool ComputeShader::isGood() const {
+	return _good;
+}
+
+GLuint ComputeShader::setUniform(const std::string& name, float x, float y) const {
+	GLuint id = util::getUniform(_id, name);
+	glUniform2f(id, x, y);
+	return id;
+}
+
+void ComputeShader::workOn(GLuint bufferA, GLuint bufferB, GLuint bufferC) const {
+	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, bufferA);
+	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 2, bufferB);
+	glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 3, bufferC);
+}
+
+void ComputeShader::dispatch() const {
+	glDispatchCompute(128, 128, 1);
+}
diff --git a/src/shader/wrap/compute_shader.h b/src/shader/wrap/compute_shader.h
new file mode 100644
index 0000000..74c8270
--- /dev/null
+++ b/src/shader/wrap/compute_shader.h
@@ -0,0 +1,32 @@
+#pragma once
+
+#include <string>
+
+#include <GL/glew.h>
+
+class ComputeShader {
+private:
+	const GLuint _id;
+
+	bool _good;
+
+public:
+	struct Guard {
+		const GLuint _id;
+
+		Guard(GLuint id);
+		~Guard();
+	};
+
+	Guard use() const;
+
+	ComputeShader(const std::string& src);
+	~ComputeShader();
+
+	bool isGood() const;
+
+	GLuint setUniform(const std::string& name, float x, float y) const;
+
+	void workOn(GLuint bufferA, GLuint bufferB, GLuint bufferC) const;
+	void dispatch() const;
+};
diff --git a/src/shader/wrap/graphic_shader.cc b/src/shader/wrap/graphic_shader.cc
new file mode 100644
index 0000000..0ed37ff
--- /dev/null
+++ b/src/shader/wrap/graphic_shader.cc
@@ -0,0 +1,45 @@
+#include "graphic_shader.h"
+
+#include "shader/util.h"
+
+GraphicShader::Guard::Guard(GLuint id):
+	_id(id) {
+	glUseProgram(_id);
+}
+
+GraphicShader::Guard::~Guard() {
+	glUseProgram(0);
+}
+
+GraphicShader::Guard GraphicShader::use() const {
+	return Guard(_id);
+}
+
+GraphicShader::GraphicShader(const std::string& vertex, const std::string fragment):
+	_id(glCreateProgram()) {
+	glAttachShader(_id, util::compileShader(vertex, GL_VERTEX_SHADER));
+	glAttachShader(_id, util::compileShader(fragment, GL_FRAGMENT_SHADER));
+	glLinkProgram(_id);
+}
+
+GraphicShader::~GraphicShader() {
+	glDeleteProgram(_id);
+}
+
+GLuint GraphicShader::setUniform(const std::string& name, int value) const {
+	GLuint id = util::getUniform(_id, name);
+	glUniform1i(id, value);
+	return id;
+}
+
+GLuint GraphicShader::setUniform(const std::string& name, const std::vector<GLuint>& v) const {
+	GLuint id = util::getUniform(_id, name);
+	glUniform1iv(id, v.size(), reinterpret_cast<const GLint*>(v.data()));
+	return id;
+}
+
+GLuint GraphicShader::setUniform(const std::string& name, glm::mat4& M) const {
+	GLuint id = util::getUniform(_id, name);
+	glUniformMatrix4fv(id, 1, GL_FALSE, &M[0][0]);
+	return id;
+}
diff --git a/src/shader/wrap/graphic_shader.h b/src/shader/wrap/graphic_shader.h
new file mode 100644
index 0000000..25a5efb
--- /dev/null
+++ b/src/shader/wrap/graphic_shader.h
@@ -0,0 +1,29 @@
+#pragma once
+
+#include <vector>
+#include <string>
+
+#include <GL/glew.h>
+#include <glm/glm.hpp>
+
+class GraphicShader {
+private:
+	const GLuint _id;
+
+public:
+	struct Guard {
+		const GLuint _id;
+
+		Guard(GLuint id);
+		~Guard();
+	};
+
+	Guard use() const;
+
+	GraphicShader(const std::string& vertex, const std::string fragment);
+	~GraphicShader();
+
+	GLuint setUniform(const std::string& name, int value) const;
+	GLuint setUniform(const std::string& name, const std::vector<GLuint>& v) const;
+	GLuint setUniform(const std::string& name, glm::mat4& M) const;
+};