GLSLでマルチテクスチャ

#include <iostream>

#include <Windows.h>
#include "prepare_shader.hpp"
#include <gl/GL.h>
#include <gl/GLU.h>
#include <gl/freeglut.h>

#pragma comment(lib,"glew32.lib")

//ウィンドウの幅と高さ
int width, height;

GLuint buf_points;
GLuint buf_tcoord;
GLuint textureID22;
GLuint textureID44;

GLfloat mproj[16];
GLfloat mmodel[16];

GLuint programID;

void texture_setting(GLuint* texid, std::vector < GLubyte >& texdata, int TEXWIDTH, int TEXHEIGHT) {
  glGenTextures(1, texid);
  glBindTexture(GL_TEXTURE_2D, *texid);

  glPixelStorei(GL_UNPACK_ALIGNMENT, 1);

  // テクスチャの割り当て
  glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, TEXWIDTH, TEXHEIGHT, 0,
    GL_RGB, GL_UNSIGNED_BYTE, texdata.data());

  // テクスチャを拡大・縮小する方法の指定
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

}

// テクスチャ作成

void create_texture_22() {
  std::vector < GLubyte > texdata;
  push_3(texdata, 255, 0, 0);
  push_3(texdata, 0, 255, 0);
  push_3(texdata, 255, 255, 255);
  push_3(texdata, 0, 255, 255);
  texture_setting(&textureID22, texdata, 2, 2);
  texdata.clear();

}
void create_texture_44() {
  std::vector < GLubyte > texdata;
  push_3(texdata, 255, 0, 0);
  push_3(texdata, 0, 0, 0);
  push_3(texdata, 255, 0, 0);
  push_3(texdata, 0, 0, 0);

  push_3(texdata, 0, 0, 0);
  push_3(texdata, 255, 0, 0);
  push_3(texdata, 0, 0, 0);
  push_3(texdata, 255, 0, 0);

  push_3(texdata, 255, 0, 0);
  push_3(texdata, 0, 0, 0);
  push_3(texdata, 255, 0, 0);
  push_3(texdata, 0, 0, 0);

  push_3(texdata, 0, 0, 0);
  push_3(texdata, 255, 0, 0);
  push_3(texdata, 0, 0, 0);
  push_3(texdata, 255, 0, 0);
  texture_setting(&textureID44, texdata, 4, 4);
  texdata.clear();
}

// シェーダとデータの設定
void init() {

  /////////////////////////////////////////////
  std::vector<GLfloat> points;
  GLfloat v = 0.8;
  push_3(points, -v , -v , 0);
  push_3(points,  v , -v , 0);
  push_3(points, -v ,  v , 0);
  push_3(points,  v ,  v , 0);
  prepare_buffer(&buf_points, points.data(), points.size() * sizeof(GLfloat), GL_STATIC_DRAW);

  /////////////////////////////////////////////
  // テクスチャ座標
  std::vector<GLfloat> texcoord;
  push_2(texcoord, 0, 0);
  push_2(texcoord, 1, 0);
  push_2(texcoord, 0, 1);
  push_2(texcoord, 1, 1);
  prepare_buffer(&buf_tcoord, texcoord.data(), texcoord.size() * sizeof(GLfloat), GL_STATIC_DRAW);
  /////////////////////////////////////////////

  //テクスチャ（画像）作成

  create_texture_22();

  create_texture_44();

  /////////////////////////////////////////////

  GLuint vtxShader;
  GLuint flagShaderR;
  const char* vtxfile = "default.vert";
  const char* fragfileR = "default.frag";

  std::string verr;
  std::string ferr;
  prepare_shader_byfile(&vtxShader, GL_VERTEX_SHADER, vtxfile, &verr);
  prepare_shader_byfile(&flagShaderR, GL_FRAGMENT_SHADER, fragfileR, &ferr);

  std::cout << verr << std::endl;
  std::cout << ferr << std::endl;

  std::string linkerr;
  link_program(&programID, { vtxShader ,flagShaderR }, nullptr, &linkerr);

  loadidentity44(mproj);
  loadidentity44(mmodel);
}

//描画関数
void disp(void) {

  glViewport(0, 0, width, height);

  glClearColor(0.2, 0.2, 0.2, 1);
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glUseProgram(programID);
  GLuint loc_ModelViewMatrix = glGetUniformLocation(programID, "ModelViewMatrix");
  GLuint loc_ProjectionMatrix = glGetUniformLocation(programID, "ProjectionMatrix");
  glUniformMatrix4fv(loc_ModelViewMatrix, 1, GL_FALSE, mmodel);
  glUniformMatrix4fv(loc_ProjectionMatrix, 1, GL_FALSE, mproj);

  GLint loc_tex22 = glGetUniformLocation(programID, "Tex22");
  glUniform1i(loc_tex22, 0);// Texture unit 0
  glActiveTexture(GL_TEXTURE0 + 0); // Texture unit 0
  glBindTexture(GL_TEXTURE_2D, textureID22);

  GLint loc_tex44 = glGetUniformLocation(programID, "Tex44");
  glUniform1i(loc_tex44, 1);// Texture unit 1
  glActiveTexture(GL_TEXTURE0 + 1); // Texture unit 1
  glBindTexture(GL_TEXTURE_2D, textureID44);

  {

    auto bind_points = EnableAndBindFArrayBuffer(0, buf_points, 3, GL_FLOAT);

    auto bind_tcoord = EnableAndBindFArrayBuffer(1, buf_tcoord, 2, GL_FLOAT);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);


  }
  glUseProgram(0);

  glFlush();
}

//ウィンドウサイズの変化時に呼び出される
void reshape(int w, int h) {
  width = w; height = h;

  disp();
}

//エントリポイント
int main(int argc, char** argv)
{
  glutInit(&argc, argv);
  glutInitWindowPosition(100, 50);
  glutInitWindowSize(500, 500);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA);

  glutCreateWindow("sample");
  glutDisplayFunc(disp);
  glutReshapeFunc(reshape);

  glewInit();

  init();

  glutMainLoop();

  return 0;
}

#version 460 core

layout (location = 0) in vec3 aPos;//ポリゴンの頂点座標
layout (location = 1) in vec2 texcd;//座標に対応するテクスチャ座標

out vec2 vTexCoord;//テクスチャ座標の出力先

uniform mat4 gl_ModelViewMatrix;
uniform mat4 gl_ProjectionMatrix;

void main()
{
  gl_Position = gl_ProjectionMatrix * gl_ModelViewMatrix * vec4(aPos, 1.0);
  vTexCoord = texcd;//フラグメントシェーダへテクスチャ座標を渡す
}

#version 460 core

out vec4 FragColor;//色の出力先

uniform sampler2D Tex22;
uniform sampler2D Tex44;
  
in vec2 vTexCoord;//頂点シェーダから渡されたテクスチャ座標

void main()
{

  //テクスチャデータとテクスチャ座標から色を決定
  vec4 c22 = texture(Tex22,vTexCoord);
  vec4 c44 = texture(Tex44,vTexCoord);

  //合成したテクスチャの色を作成
  vec4 crr;
  crr.x = c44.x * c22.x;
  crr.y = c44.x * c22.y;
  crr.z = c44.x * c22.z;
  
  FragColor = crr;
}