OGLplus (0.52.0) a C++ wrapper for OpenGL

oglplus/019_gs_tessell.cpp

Shows how to do simple tessellation with the geometry shader

019_gs_tessell.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 "example.hpp"
namespace oglplus {
class TessellationExample : public Example
{
private:
// helper object building shape vertex attributes
shapes::SimpleIcosahedron make_shape;
// helper object encapsulating shape drawing instructions
shapes::DrawingInstructions shape_instr;
// indices pointing to shape primitive elements
// wrapper around the current OpenGL context
Context gl;
// Shaders
// Program
Program prog;
// Handles for uniforms in prog
Uniform<GLint> tess_level;
Uniform<Vec2f> viewport_dimensions;
Uniform<Mat4f> projection_matrix, camera_matrix, model_matrix;
// A vertex array object for the rendered shape
VertexArray shape;
// VBOs for the shape's vertices and element indices
Buffer verts, indices;
public:
TessellationExample(void)
: shape_instr(make_shape.Instructions())
, shape_indices(make_shape.Indices())
, tess_level(prog)
, viewport_dimensions(prog)
, projection_matrix(prog)
, camera_matrix(prog)
, model_matrix(prog)
{
vs.Source(
"#version 330\n"
"in vec4 Position;"
"void main(void)"
"{"
" gl_Position = Position;"
"}"
);
vs.Compile();
gs.Source(
"#version 330\n"
"layout (triangles) in;"
"layout (triangle_strip, max_vertices = 48) out;"
"const vec3 LightPosition = vec3(12.0, 10.0, 7.0);"
"uniform mat4 ProjectionMatrix, CameraMatrix, ModelMatrix;"
"uniform vec2 ViewportDimensions;"
"uniform int TessLevel;"
"noperspective out vec3 geomDist;"
"flat out vec3 geomNormal;"
"out vec3 geomColor;"
"out vec3 geomLightDir;"
"void make_triangle(vec4 p0, vec4 p1, vec4 p2)"
"{"
" vec3 n0 = (ModelMatrix*vec4(p0.xyz, 0)).xyz;"
" vec3 n1 = (ModelMatrix*vec4(p1.xyz, 0)).xyz;"
" vec3 n2 = (ModelMatrix*vec4(p2.xyz, 0)).xyz;"
" vec4 m0 = ModelMatrix*p0;"
" vec4 m1 = ModelMatrix*p1;"
" vec4 m2 = ModelMatrix*p2;"
" vec4 c0 = ProjectionMatrix*CameraMatrix*m0;"
" vec4 c1 = ProjectionMatrix*CameraMatrix*m1;"
" vec4 c2 = ProjectionMatrix*CameraMatrix*m2;"
" vec2 s0 = ViewportDimensions * c0.xy/c0.w;"
" vec2 s1 = ViewportDimensions * c1.xy/c1.w;"
" vec2 s2 = ViewportDimensions * c2.xy/c2.w;"
" vec2 v0 = s2 - s1;"
" vec2 v1 = s0 - s2;"
" vec2 v2 = s1 - s0;"
" float d0 = abs(v1.x*v2.y-v1.y*v2.x)/length(v0);"
" float d1 = abs(v2.x*v0.y-v2.y*v0.x)/length(v1);"
" float d2 = abs(v0.x*v1.y-v0.y*v1.x)/length(v2);"
" geomNormal = normalize(n0+n1+n2);"
" gl_Position = c0;"
" geomColor = normalize(abs(vec3(1, 1, 1) - n0));"
" geomLightDir = LightPosition - m0.xyz;"
" geomDist = vec3(d0, 0.0, 0.0);"
" EmitVertex();"
" gl_Position = c1;"
" geomColor = normalize(abs(vec3(1, 1, 1) - n1));"
" geomLightDir = LightPosition - m1.xyz;"
" geomDist = vec3(0.0, d1, 0.0);"
" EmitVertex();"
" gl_Position = c2;"
" geomColor = normalize(abs(vec3(1, 1, 1) - n2));"
" geomLightDir = LightPosition - m2.xyz;"
" geomDist = vec3(0.0, 0.0, d2);"
" EmitVertex();"
" EndPrimitive();"
"}"
"void do_tess_1(vec4 p_0, vec4 p_1, vec4 p_2, int l)"
"{"
" if(l == 1) make_triangle(p_0, p_1, p_2);"
" else"
" {"
" vec4 p01 = vec4(normalize(p_0.xyz+p_1.xyz), 1.0);"
" vec4 p12 = vec4(normalize(p_1.xyz+p_2.xyz), 1.0);"
" vec4 p20 = vec4(normalize(p_2.xyz+p_0.xyz), 1.0);"
" make_triangle(p_0, p01, p20);"
" make_triangle(p01, p_1, p12);"
" make_triangle(p20, p12, p_2);"
" make_triangle(p01, p12, p20);"
" }"
"}"
"void do_tess_0(vec4 p_0, vec4 p_1, vec4 p_2, int l)"
"{"
" if(l == 0) make_triangle(p_0, p_1, p_2);"
" else"
" {"
" vec4 p01 = vec4(normalize(p_0.xyz+p_1.xyz), 1.0);"
" vec4 p12 = vec4(normalize(p_1.xyz+p_2.xyz), 1.0);"
" vec4 p20 = vec4(normalize(p_2.xyz+p_0.xyz), 1.0);"
" do_tess_1(p_0, p01, p20, l);"
" do_tess_1(p01, p_1, p12, l);"
" do_tess_1(p20, p12, p_2, l);"
" do_tess_1(p01, p12, p20, l);"
" }"
"}"
"void main(void)"
"{"
" do_tess_0("
" gl_in[0].gl_Position,"
" gl_in[1].gl_Position,"
" gl_in[2].gl_Position,"
" TessLevel"
" );"
"}"
);
gs.Compile();
fs.Source(
"#version 330\n"
"noperspective in vec3 geomDist;"
"flat in vec3 geomNormal;"
"in vec3 geomColor;"
"in vec3 geomLightDir;"
"out vec3 fragColor;"
"void main(void)"
"{"
" float MinDist = min(min(geomDist.x,geomDist.y),geomDist.z);"
" float EdgeAlpha = exp2(-pow(MinDist, 2.0));"
" const float Ambient = 0.7;"
" float Diffuse = max(dot("
" normalize(geomNormal),"
" normalize(geomLightDir)"
" )+0.1, 0.0)*1.4;"
" vec3 FaceColor = geomColor * (Diffuse + Ambient);"
" const vec3 EdgeColor = vec3(0.0, 0.0, 0.0);"
" fragColor = mix(FaceColor, EdgeColor, EdgeAlpha);"
"}"
);
fs.Compile();
prog.AttachShader(vs);
prog.AttachShader(gs);
prog.AttachShader(fs);
prog.Link();
prog.Use();
tess_level.BindTo("TessLevel");
viewport_dimensions.BindTo("ViewportDimensions");
projection_matrix.BindTo("ProjectionMatrix");
camera_matrix.BindTo("CameraMatrix");
model_matrix.BindTo("ModelMatrix");
shape.Bind();
verts.Bind(Buffer::Target::Array);
{
std::vector<GLfloat> data;
GLuint n_per_vertex = make_shape.Positions(data);
Buffer::Data(Buffer::Target::Array, data);
VertexArrayAttrib attr(prog, "Position");
attr.Setup<GLfloat>(n_per_vertex);
attr.Enable();
indices.Bind(Buffer::Target::ElementArray);
Buffer::Data(Buffer::Target::ElementArray, shape_indices);
shape_indices.clear();
}
//
gl.ClearColor(0.7f, 0.7f, 0.7f, 0.0f);
gl.ClearDepth(1.0f);
prog.Use();
}
void Reshape(GLuint width, GLuint height)
{
gl.Viewport(width, height);
viewport_dimensions.Set(Vec2f(width, height));
projection_matrix.Set(
Degrees(60),
double(width)/height,
1, 50
)
);
}
void Render(double time)
{
gl.Clear().ColorBuffer().DepthBuffer();
//
auto camera = CamMatrixf::Orbiting(
Vec3f(),
15.0 - SineWave(time / 13)*8.0,
Degrees(time * 33),
Degrees(SineWave(time / 21.0) * 31)
);
camera_matrix.Set(camera);
const Vec3f offsets[4] = {
Vec3f( 2, 0, 0),
Vec3f(-2, 0, 0),
Vec3f( 0, 0, 2),
Vec3f( 0, 0,-2)
};
for(int i=0; i!=4; ++i)
{
auto model =
ModelMatrixf::RotationX(Degrees(time * 11))*
ModelMatrixf::RotationZ(Degrees(time * (37+3*i)));
GLint level = GLint(17.0 / (Length((
Inverse(model)*
Vec4f(camera.Position(), 1)
).xyz())+0.1));
model_matrix.Set(model);
tess_level.Set(level);
shape_instr.Draw(shape_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 TessellationExample);
}
} // 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).