text: /******************************************************************************
   * The MIT License (MIT)
   *
   * Copyright (c) 2015-2019 Baldur Karlsson
   *
   * Permission is hereby granted, free of charge, to any person obtaining a copy
   * of this software and associated documentation files (the "Software"), to deal
   * in the Software without restriction, including without limitation the rights
   * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
   * copies of the Software, and to permit persons to whom the Software is
   * furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in
   * all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
   * THE SOFTWARE.
   ******************************************************************************/
  
  #include "gl_test.h"
  
  struct GL_Mip_Gen_RT : OpenGLGraphicsTest
  {
    static constexpr const char *Description =
        "Tests rendering from one mip to another to do a downsample chain";
  
    std::string vertex = R"EOSHADER(
  #version 420 core
  
  out vec2 uv;
  
  void main()
  {
    const vec4 verts[4] = vec4[4](vec4(-1.0, -1.0, 0.5, 1.0), vec4(1.0, -1.0, 0.5, 1.0),
                                  vec4(-1.0, 1.0, 0.5, 1.0), vec4(1.0, 1.0, 0.5, 1.0));
  
    gl_Position = verts[gl_VertexID];
    uv = gl_Position.xy * 0.5f + 0.5f;
  }
  
  )EOSHADER";
  
    std::string pixel = R"EOSHADER(
  #version 420 core
  
  in vec2 uv;
  
  layout(location = 0, index = 0) out vec4 Color;
  
  layout(binding = 0) uniform sampler2D tex2D;
  
  void main()
  {
  	Color = textureLod(tex2D, -uv, 0.0f);
  }
  
  )EOSHADER";
  
    int main(int argc, char **argv)
    {
      // initialise, create window, create context, etc
      if(!Init(argc, argv))
        return 3;
  
      GLuint vao = MakeVAO();
      glBindVertexArray(vao);
  
      GLuint vb = MakeBuffer();
      glBindBuffer(GL_ARRAY_BUFFER, vb);
      glBufferStorage(GL_ARRAY_BUFFER, sizeof(DefaultTri), DefaultTri, 0);
  
      glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(DefaultA2V), (void *)(0));
      glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, sizeof(DefaultA2V), (void *)(sizeof(Vec3f)));
      glVertexAttribPointer(2, 2, GL_FLOAT, GL_FALSE, sizeof(DefaultA2V),
                            (void *)(sizeof(Vec3f) + sizeof(Vec4f)));
  
      glEnableVertexAttribArray(0);
      glEnableVertexAttribArray(1);
      glEnableVertexAttribArray(2);
  
      GLuint program = MakeProgram(vertex, pixel);
      glObjectLabel(GL_PROGRAM, program, -1, "Full program");
  
      GLuint tex = MakeTexture();
      glBindTexture(GL_TEXTURE_2D, tex);
      glTexStorage2D(GL_TEXTURE_2D, 8, GL_SRGB8_ALPHA8, 1024, 1024);
  
      GLuint fbo[8];
      for(int i = 0; i < 8; i++)
      {
        fbo[i] = MakeFBO();
        glBindFramebuffer(GL_FRAMEBUFFER, fbo[i]);
        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, tex, i);
      }
  
      // fill upper mip with colour ramp
      uint32_t *ramp = new uint32_t[1024 * 1024];
      for(uint32_t i = 0; i < 1024 * 1024; i++)
      {
        float x = float(i % 1024);
        float y = float(i / 1024);
        ramp[i] = uint32_t(uint32_t(255.0f * (x / 1024.0f)) | (uint32_t(255.0f * (y / 1024.0f)) << 8) |
                           (uint32_t(255.0f * ((x + y) / 2048.0f)) << 16) | 0xff000000);
      }
  
      while(Running())
      {
        float col[] = {0.4f, 0.5f, 0.6f, 1.0f};
        glBindFramebuffer(GL_FRAMEBUFFER, 0);
        glClearBufferfv(GL_COLOR, 0, col);
  
        // clear all FBOs
        for(int i = 0; i < 8; i++)
        {
          glBindFramebuffer(GL_FRAMEBUFFER, fbo[i]);
          glClearBufferfv(GL_COLOR, 0, col);
        }
  
        glBindFramebuffer(GL_FRAMEBUFFER, 0);
  
        glBindVertexArray(vao);
  
        glUseProgram(program);
  
        {
          // view first mip and upload data
          glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
          glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);
          glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 1024, 1024, GL_RGBA, GL_UNSIGNED_BYTE, ramp);
  
          for(int i = 1; i < 8; i++)
          {
            // bind relevant fbo
            glBindFramebuffer(GL_FRAMEBUFFER, fbo[i]);
  
            // change texture parameters to view previous mip
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, i - 1);
            glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, i - 1);
  
            // set viewport
            glViewport(0, 0, 1024 >> i, 1024 >> i);
  
            // do downsample
            glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
          }
  
          // reset texture parameters to default
          glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_BASE_LEVEL, 0);
          glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 0);
  
          // bind default framebuffer
          glBindFramebuffer(GL_FRAMEBUFFER, 0);
        }
  
        Present();
      }
  
      delete[] ramp;
  
      return 0;
    }
  };
  
  REGISTER_TEST(GL_Mip_Gen_RT);