OGLplus (0.52.0) a C++ wrapper for OpenGL

oglplus/014_multi_cube_gs.cpp

Shows how to draw multiple instances of a cube using geometry shader

014_multi_cube_gs.png

Copyright 2008-2014 Matus Chochlik. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#include <oglplus/gl.hpp>
#include <oglplus/all.hpp>
#include <cmath>
#include "example.hpp"
namespace oglplus {
class CubeExample : public Example
{
private:
// helper object building cube vertex attributes
shapes::Cube make_cube;
// helper object encapsulating cube drawing instructions
shapes::DrawingInstructions cube_instr;
// indices pointing to cube primitive elements
// wrapper around the current OpenGL context
Context gl;
// Vertex shader
// Geometry shader
// Fragment shader
// Program
Program prog;
// Handle for uniforms in program
Uniform<Mat4f> projection_matrix, camera_matrix;
// A vertex array object for the rendered cube
// VBOs for the cube's vertices
Buffer verts;
public:
CubeExample(void)
: cube_instr(make_cube.Instructions())
, cube_indices(make_cube.Indices())
, projection_matrix(prog)
, camera_matrix(prog)
{
// Set the vertex shader source and compile it
vs.Source(
"#version 330\n"
"in vec4 Position;"
"void main(void)"
"{"
" gl_Position = Position;"
"}"
).Compile();
// Set the geometry shader source and compile it
gs.Source(
"#version 330\n"
"layout(triangles) in;"
"layout(triangle_strip, max_vertices = 108) out;"
"uniform mat4 ProjectionMatrix, CameraMatrix;"
"out vec3 vertColor;"
"void main(void)"
"{"
" for(int c=0; c!=36; ++c)"
" {"
" float angle = c * 10 * 2 * 3.14159 / 360.0;"
" float cx = cos(angle);"
" float sx = sin(angle);"
" mat4 ModelMatrix = mat4("
" cx, 0.0, sx, 0.0,"
" 0.0, 1.0, 0.0, 0.0,"
" -sx, 0.0, cx, 0.0,"
" 0.0, 0.0, 0.0, 1.0 "
" ) * mat4("
" 1.0, 0.0, 0.0, 0.0,"
" 0.0, 1.0, 0.0, 0.0,"
" 0.0, 0.0, 1.0, 0.0,"
" 12.0, 0.0, 0.0, 1.0 "
" );"
" for(int v=0; v!=gl_in.length(); ++v)"
" {"
" vec4 vert = gl_in[v].gl_Position;"
" gl_Position = "
" ProjectionMatrix *"
" CameraMatrix *"
" ModelMatrix *"
" vert;"
" vertColor = abs(normalize(ModelMatrix*vert)).xzy;"
" EmitVertex();"
" }"
" EndPrimitive();"
" }"
"}"
).Compile();
// set the fragment shader source and compile it
fs.Source(
"#version 330\n"
"in vec3 vertColor;"
"out vec4 fragColor;"
"void main(void)"
"{"
" fragColor = vec4(vertColor, 1.0);"
"}"
).Compile();
// attach the shaders to the program
prog << vs << gs << fs;
// link and use it
prog.Link().Use();
projection_matrix.BindTo("ProjectionMatrix");
camera_matrix.BindTo("CameraMatrix");
// bind the VAO for the cube
cube.Bind();
// bind the VBO for the cube vertices
verts.Bind(Buffer::Target::Array);
{
std::vector<GLfloat> data;
GLuint n_per_vertex = make_cube.Positions(data);
// upload the data
Buffer::Data(Buffer::Target::Array, data);
// setup the vertex attribs array for the vertices
VertexArrayAttrib attr(prog, "Position");
attr.Setup<GLfloat>(n_per_vertex).Enable();
}
gl.ClearColor(0.9f, 0.9f, 0.9f, 0.0f);
gl.ClearDepth(1.0f);
}
void Reshape(GLuint width, GLuint height)
{
gl.Viewport(width, height);
prog.Use();
projection_matrix.Set(
Degrees(70),
double(width)/height,
1, 50
)
);
}
void Render(double time)
{
gl.Clear().ColorBuffer().DepthBuffer();
//
// set the matrix for camera orbiting the origin
camera_matrix.Set(
Vec3f(),
18.5,
Degrees(time * 135),
Degrees(SineWave(time / 20.0) * 30)
)
);
// draw 1 instance of the cube
// the geometry shader will spawn 36 copies
// and take care of their placement
cube_instr.Draw(cube_indices);
}
bool Continue(double time)
{
return time < 30.0;
}
};
void setupExample(ExampleParams& /*params*/){ }
std::unique_ptr<ExampleThread> makeExampleThread(
Example& /*example*/,
unsigned /*thread_id*/,
const ExampleParams& /*params*/
){ return std::unique_ptr<ExampleThread>(); }
std::unique_ptr<Example> makeExample(const ExampleParams& /*params*/)
{
return std::unique_ptr<Example>(new CubeExample);
}
} // namespace oglplus

Copyright © 2010-2014 Matúš Chochlík, University of Žilina, Žilina, Slovakia.
<matus.chochlik -at- fri.uniza.sk>
<chochlik -at -gmail.com>
Documentation generated on Mon Sep 22 2014 by Doxygen (version 1.8.6).