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Purpose of the Sample:

Demonstrates how to use the stencil buffer to mask draw calls. Over time, a portion of the man’s body will be rendered in wireframe. The effect is achieved like so.

Draw Filled Man
1. Write 0 to the stencil buffer for each fragment rendered to by the filled man.
Render an invisible quad in front of the man.
1. Write 1 to the stencil buffer for each fragment rendered to by the quad.
Render the Wireframe Man
1. Only display the wireframe man where the stencil buffer value is 1 which is wherever the quad was rendered.

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Captured with RenderDoc Version 1.2 (x86) (x64)

CGame.h

#ifndef __CGAME__
#define __CGAME__

#include <glad/glad.h>
#include "shader_s.h"

class Model;

class CGame
{
public:
    CGame() {};

    void Initialize(unsigned int screenWidth, unsigned int screenHeight);
    void Shutdown();
    void Render();

    void OnResize(int screenWidth, int screenHeight);

private:
    void SetupGPUProgram();
    void SetupModel();

    Shader* m_pShaderPass0;
    Shader* m_pShaderPass1;
    Shader* m_pShaderStencilPass;
    Model* m_pManModel;
    Model* m_pStencilModel;

    unsigned int m_Width;
    unsigned int m_Height;
};

#endif

#ifndef __CGAME__

#define __CGAME__

#include <glad/glad.h>

#include "shader_s.h"

class Model;

class CGame

{

public:

CGame() {};

void Initialize(unsigned int screenWidth, unsigned int screenHeight);

void Shutdown();

void Render();

void OnResize(int screenWidth, int screenHeight);

private:

void SetupGPUProgram();

void SetupModel();

Shader* m_pShaderPass0;

Shader* m_pShaderPass1;

Shader* m_pShaderStencilPass;

Model* m_pManModel;

Model* m_pStencilModel;

unsigned int m_Width;

unsigned int m_Height;

};

#endif

CGame.cpp

#include "CGame.h"

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image/stb_image.h"
#include "Model.h"
#include "Mesh.h"
#include "glm/mat4x4.hpp"
#include "glm/vec3.hpp"
#include "glm/glm.hpp"
#include "glm/gtc/matrix_transform.hpp"
#include "glm/gtc/type_ptr.hpp"
#include <chrono>

void CGame::Initialize(unsigned int screenWidth, unsigned int screenHeight)
{
    m_Width = screenWidth;
    m_Height = screenHeight;

    SetupGPUProgram();
    SetupModel();

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
    glEnable(GL_STENCIL_TEST);
}

void CGame::Shutdown()
{
    
}

void CGame::OnResize(int width, int height)
{
    m_Width = width;
    m_Height = height;

    glViewport(0, 0, m_Width, m_Height);
    glScissor(0, 0, m_Width, m_Height);
}

void CGame::Render()
{
    static auto startTime = std::chrono::high_resolution_clock::now();

    auto currentTime = std::chrono::high_resolution_clock::now();
    float time = std::chrono::duration<float, std::chrono::seconds::period>(currentTime - startTime).count();

    glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
    glClearDepth(1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
    glColorMask(1, 1, 1, 1);

    // Draw the Filled Man
    glEnable(GL_STENCIL_TEST);
    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
    glStencilFunc(GL_ALWAYS, 0, 0xFF); // all fragments should update the stencil buffer
    glStencilMask(0xFF); // enable writing to the stencil buffer
    glm::mat4 model = glm::rotate(glm::mat4(1.0f), time * glm::radians(90.0f), glm::vec3(0.0f, 1.0f, 0.0f));
    glm::mat4 view;
    view = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, -2.0f, -10.0f));
    glm::mat4 projection;
    projection = glm::perspective(glm::radians(60.0f), m_Width / static_cast<float>(m_Height), 0.03f, 100.0f);
    glm::mat4 mvp = projection * view * model;

    m_pShaderPass0->use();
    m_pShaderPass0->setMatrix4x4("modelMatrix", glm::value_ptr(model));
    m_pShaderPass0->setMatrix4x4("viewMatrix", glm::value_ptr(view));
    m_pShaderPass0->setMatrix4x4("projectionMatrix", glm::value_ptr(projection));
    m_pShaderPass0->setMatrix4x4("mvpMatrix", glm::value_ptr(mvp));
    m_pShaderPass0->setFloat("time", time);
    glDepthFunc(GL_LEQUAL);
    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
    m_pManModel->meshes[0].Draw(*m_pShaderPass0);

    // Draw the Stencil Quad
    glStencilMask(0xFF);
    model = glm::rotate(glm::mat4(1.0f), glm::radians(90.0f), glm::vec3(1.0f, 0.0f, 0.0f));
    model = glm::translate(model, glm::vec3(0.0f, 4.0f, -2.5f));
    model = glm::scale(model, glm::vec3(1.0f, 1.0f, 1.0f));
    mvp = projection * view * model;
    m_pShaderStencilPass->use();
    m_pShaderStencilPass->setFloat("time", time);
    m_pShaderStencilPass->setMatrix4x4("mvpMatrix", glm::value_ptr(mvp));
    glDepthFunc(GL_ALWAYS);
    glDepthMask(0);
    glStencilFunc(GL_ALWAYS, 1, 0xFF);
    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);
    glColorMask(0, 0, 0, 0);
    m_pStencilModel->meshes[0].Draw(*m_pShaderStencilPass);
    glDepthFunc(GL_LEQUAL);
    glDepthMask(1);
    glColorMask(1, 1, 1, 1);

    // Draw the Wireframe man
    model = glm::rotate(glm::mat4(1.0f), time * glm::radians(90.0f), glm::vec3(0.0f, 1.0f, 0.0f));
    view = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, -2.0f, -10.0f));
    projection = glm::perspective(glm::radians(60.0f), m_Width / static_cast<float>(m_Height), 0.03f, 100.0f);
    mvp = projection * view * model;
    m_pShaderPass1->use();
    m_pShaderPass1->setMatrix4x4("modelMatrix", glm::value_ptr(model));
    m_pShaderPass1->setMatrix4x4("viewMatrix", glm::value_ptr(view));
    m_pShaderPass1->setMatrix4x4("projectionMatrix", glm::value_ptr(projection));
    m_pShaderPass1->setMatrix4x4("mvpMatrix", glm::value_ptr(mvp));
    m_pShaderPass1->setFloat("time", time);

    glStencilFunc(GL_EQUAL, 1, 0xFF);
    glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);

    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    m_pManModel->meshes[0].Draw(*m_pShaderPass1);
}

void CGame::SetupModel()
{
    m_pManModel = new Model();
    m_pManModel->Load("man.obj");

    m_pStencilModel = new Model();
    m_pStencilModel->Load("quad.obj");
}

void CGame::SetupGPUProgram()
{
    m_pShaderPass0 = new Shader("vertexPass0.glsl", "fragmentPass0.glsl");
    m_pShaderPass1 = new Shader("vertexPass1.glsl", "fragmentPass1.glsl");
    m_pShaderStencilPass = new Shader("vertexStencil.glsl", "fragmentStencil.glsl");
}

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#include "CGame.h"

#define STB_IMAGE_IMPLEMENTATION

#include "stb_image/stb_image.h"

#include "Model.h"

#include "Mesh.h"

#include "glm/mat4x4.hpp"

#include "glm/vec3.hpp"

#include "glm/glm.hpp"

#include "glm/gtc/matrix_transform.hpp"

#include "glm/gtc/type_ptr.hpp"

#include <chrono>

void CGame::Initialize(unsigned int screenWidth, unsigned int screenHeight)

{

m_Width = screenWidth;

m_Height = screenHeight;

SetupGPUProgram();

SetupModel();

glEnable(GL_DEPTH_TEST);

glDepthFunc(GL_LEQUAL);

glEnable(GL_STENCIL_TEST);

}

void CGame::Shutdown()

{

}

void CGame::OnResize(int width, int height)

{

m_Width = width;

m_Height = height;

glViewport(0, 0, m_Width, m_Height);

glScissor(0, 0, m_Width, m_Height);

}

void CGame::Render()

{

static auto startTime = std::chrono::high_resolution_clock::now();

auto currentTime = std::chrono::high_resolution_clock::now();

float time = std::chrono::duration<float, std::chrono::seconds::period>(currentTime - startTime).count();

glClearColor(0.2f, 0.3f, 0.3f, 1.0f);

glClearDepth(1.0f);

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

glColorMask(1, 1, 1, 1);

// Draw the Filled Man

glEnable(GL_STENCIL_TEST);

glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);

glStencilFunc(GL_ALWAYS, 0, 0xFF); // all fragments should update the stencil buffer

glStencilMask(0xFF); // enable writing to the stencil buffer

glm::mat4 model = glm::rotate(glm::mat4(1.0f), time * glm::radians(90.0f), glm::vec3(0.0f, 1.0f, 0.0f));

glm::mat4 view;

view = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, -2.0f, -10.0f));

glm::mat4 projection;

projection = glm::perspective(glm::radians(60.0f), m_Width / static_cast<float>(m_Height), 0.03f, 100.0f);

glm::mat4 mvp = projection * view * model;

m_pShaderPass0->use();

m_pShaderPass0->setMatrix4x4("modelMatrix", glm::value_ptr(model));

m_pShaderPass0->setMatrix4x4("viewMatrix", glm::value_ptr(view));

m_pShaderPass0->setMatrix4x4("projectionMatrix", glm::value_ptr(projection));

m_pShaderPass0->setMatrix4x4("mvpMatrix", glm::value_ptr(mvp));

m_pShaderPass0->setFloat("time", time);

glDepthFunc(GL_LEQUAL);

glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);

m_pManModel->meshes[0].Draw(*m_pShaderPass0);

// Draw the Stencil Quad

glStencilMask(0xFF);

model = glm::rotate(glm::mat4(1.0f), glm::radians(90.0f), glm::vec3(1.0f, 0.0f, 0.0f));

model = glm::translate(model, glm::vec3(0.0f, 4.0f, -2.5f));

model = glm::scale(model, glm::vec3(1.0f, 1.0f, 1.0f));

mvp = projection * view * model;

m_pShaderStencilPass->use();

m_pShaderStencilPass->setFloat("time", time);

m_pShaderStencilPass->setMatrix4x4("mvpMatrix", glm::value_ptr(mvp));

glDepthFunc(GL_ALWAYS);

glDepthMask(0);

glStencilFunc(GL_ALWAYS, 1, 0xFF);

glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);

glColorMask(0, 0, 0, 0);

m_pStencilModel->meshes[0].Draw(*m_pShaderStencilPass);

glDepthFunc(GL_LEQUAL);

glDepthMask(1);

glColorMask(1, 1, 1, 1);

// Draw the Wireframe man

model = glm::rotate(glm::mat4(1.0f), time * glm::radians(90.0f), glm::vec3(0.0f, 1.0f, 0.0f));

view = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, -2.0f, -10.0f));

projection = glm::perspective(glm::radians(60.0f), m_Width / static_cast<float>(m_Height), 0.03f, 100.0f);

mvp = projection * view * model;

m_pShaderPass1->use();

m_pShaderPass1->setMatrix4x4("modelMatrix", glm::value_ptr(model));

m_pShaderPass1->setMatrix4x4("viewMatrix", glm::value_ptr(view));

m_pShaderPass1->setMatrix4x4("projectionMatrix", glm::value_ptr(projection));

m_pShaderPass1->setMatrix4x4("mvpMatrix", glm::value_ptr(mvp));

m_pShaderPass1->setFloat("time", time);

glStencilFunc(GL_EQUAL, 1, 0xFF);

glStencilOp(GL_KEEP, GL_KEEP, GL_REPLACE);

glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);

m_pManModel->meshes[0].Draw(*m_pShaderPass1);

}

void CGame::SetupModel()

{

m_pManModel = new Model();

m_pManModel->Load("man.obj");

m_pStencilModel = new Model();

m_pStencilModel->Load("quad.obj");

}

void CGame::SetupGPUProgram()

{

m_pShaderPass0 = new Shader("vertexPass0.glsl", "fragmentPass0.glsl");

m_pShaderPass1 = new Shader("vertexPass1.glsl", "fragmentPass1.glsl");

m_pShaderStencilPass = new Shader("vertexStencil.glsl", "fragmentStencil.glsl");

}

vertexPass0.glsl – Draw the Filled Man

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 normal;

uniform mat4 modelMatrix;
uniform mat4 viewMatrix;
uniform mat4 projectionMatrix;
uniform mat4 mvpMatrix;
uniform float time;

out vec4 fsNormal;

void main()
{
    vec4 pos = mvpMatrix * vec4(position.xyz, 1);
    fsNormal = vec4(normal.xyz, 0);
    gl_Position = pos;
}

#version 330 core

layout (location = 0) in vec3 position;

layout (location = 1) in vec3 normal;

uniform mat4 modelMatrix;

uniform mat4 viewMatrix;

uniform mat4 projectionMatrix;

uniform mat4 mvpMatrix;

uniform float time;

out vec4 fsNormal;

void main()

{

vec4 pos = mvpMatrix * vec4(position.xyz, 1);

fsNormal = vec4(normal.xyz, 0);

gl_Position = pos;

}

fragmentPass0.glsl – Shade the Filled Man with his Normals

#version 330 core
out vec4 FragColor;

in vec4 fsNormal;

void main()
{
    vec3 color = vec3(1,0,0);
    FragColor = vec4(fsNormal.rgb, 1.0f);
}

#version 330 core

out vec4 FragColor;

in vec4 fsNormal;

void main()

{

vec3 color = vec3(1,0,0);

FragColor = vec4(fsNormal.rgb, 1.0f);

}

vertexStencil.glsl – Render the Quad Mask

#version 330 core
layout (location = 0) in vec3 position;

uniform float time;
uniform mat4 mvpMatrix;

out vec4 fsNormal;

void main()
{
    vec3 newModelPos = position + vec3(0, 0, sin(time * 0.4) * 3.0);
    vec4 pos = mvpMatrix * vec4(newModelPos, 1);

    gl_Position = pos;
}

#version 330 core

layout (location = 0) in vec3 position;

uniform float time;

uniform mat4 mvpMatrix;

out vec4 fsNormal;

void main()

{

vec3 newModelPos = position + vec3(0, 0, sin(time * 0.4) * 3.0);

vec4 pos = mvpMatrix * vec4(newModelPos, 1);

gl_Position = pos;

}

fragmentStencil.glsl – Render the Quad Mask

#version 330 core
out vec4 FragColor;

void main()
{
    FragColor = vec4(0f, 0f, 0f, 1f);
}

#version 330 core

out vec4 FragColor;

void main()

{

FragColor = vec4(0f, 0f, 0f, 1f);

}

vertexPass1.glsl – Render the Wireframe Man

#version 330 core
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 normal;

uniform mat4 modelMatrix;
uniform mat4 viewMatrix;
uniform mat4 projectionMatrix;
uniform mat4 mvpMatrix;
uniform float time;

out vec4 fsNormal;

void main()
{
    vec4 pos = mvpMatrix * vec4(position.xyz, 1);
    fsNormal = vec4(normal.xyz, 0);
    gl_Position = pos;
}

#version 330 core

layout (location = 0) in vec3 position;

layout (location = 1) in vec3 normal;

uniform mat4 modelMatrix;

uniform mat4 viewMatrix;

uniform mat4 projectionMatrix;

uniform mat4 mvpMatrix;

uniform float time;

out vec4 fsNormal;

void main()

{

vec4 pos = mvpMatrix * vec4(position.xyz, 1);

fsNormal = vec4(normal.xyz, 0);

gl_Position = pos;

}

fragmentPass1.glsl – Render the Wireframe Man

#version 330 core
out vec4 FragColor;

in vec4 fsNormal;

void main()
{
    vec3 color = vec3(0,1,0);
    FragColor = vec4(color.rgb, 1.0f);
}

#version 330 core

out vec4 FragColor;

in vec4 fsNormal;

void main()

{

vec3 color = vec3(0,1,0);

FragColor = vec4(color.rgb, 1.0f);

}

xdPixel

OpenGL Stencil Buffer Effect

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Purpose of the Sample:

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CGame.h

CGame.cpp

vertexPass0.glsl – Draw the Filled Man

fragmentPass0.glsl – Shade the Filled Man with his Normals

vertexStencil.glsl – Render the Quad Mask

fragmentStencil.glsl – Render the Quad Mask

vertexPass1.glsl – Render the Wireframe Man

fragmentPass1.glsl – Render the Wireframe Man

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Practical Computer Graphics

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Purpose of the Sample:

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CGame.h

CGame.cpp

vertexPass0.glsl – Draw the Filled Man

fragmentPass0.glsl – Shade the Filled Man with his Normals

vertexStencil.glsl – Render the Quad Mask

fragmentStencil.glsl – Render the Quad Mask

vertexPass1.glsl – Render the Wireframe Man

fragmentPass1.glsl – Render the Wireframe Man

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Practical Computer Graphics

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