sol2_test/src/image.cpp

#include "image.hpp"
#include <stb_image.h>

// these never change so just put them here
float VERTICES[24] = {
  // positions   // texCoords
  -1.0f,  1.0f,  0.0f, 1.0f, // top left
  -1.0f, -1.0f,  0.0f, 0.0f, // bottom left
  1.0f, -1.0f,   1.0f, 0.0f, // bottom right

  -1.0f,  1.0f,  0.0f, 1.0f, // top left
  1.0f, -1.0f,   1.0f, 0.0f, // bottom right
  1.0f,  1.0f,   1.0f, 1.0f, // top right
};

unsigned int image_to_texture(unsigned char *data, int width, int height, int nrComponents) {
  unsigned int textureID;
  glGenTextures(1, &textureID);

  GLenum format = GL_RGB;

  switch(nrComponents) {
    case 1:
      format = GL_RED;
      break;
    case 3:
      format = GL_RGB;
      break;
    case 4:
      format = GL_RGBA;
      break;
    default:
      dbc::sentinel($F("Impossible nrComponents={} when loading image", nrComponents));
  }

  glBindTexture(GL_TEXTURE_2D, textureID);
  glTexImage2D(GL_TEXTURE_2D, 0, format, width, height, 0, format, GL_UNSIGNED_BYTE, data);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
  glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

  return textureID;
}

void Image::load(const std::string& filename) {
  stbi_set_flip_vertically_on_load(true);
  unsigned char *data = stbi_load(filename.c_str(), &width, &height, &nrComponents, 0);
  dbc::check(data != NULL, "Failed to stb_load image.");

  texture_id = image_to_texture(data, width, height, nrComponents);

  stbi_image_free(data);
}

void Image::render() {
  shader.use();
  shader.setInt("texture1", texture_id);
  glBindVertexArray(image_vao);
  glBindTexture(GL_TEXTURE_2D, texture_id);
  glDrawArrays(GL_TRIANGLES, 0, 6);

  glBindTexture(GL_TEXTURE_2D, 0);
  glBindVertexArray(0);
}

Image::Image() {
  glGenVertexArrays(1, &image_vao);
  glGenBuffers(1, &image_vbo);

  glBindVertexArray(image_vao);
  glBindBuffer(GL_ARRAY_BUFFER, image_vbo);
  glBufferData(GL_ARRAY_BUFFER, sizeof(VERTICES), &VERTICES, GL_STATIC_DRAW);

  // position attrib
  glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)0);
  glEnableVertexAttribArray(0);

  // color attribute
  glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (void*)(2 * sizeof(float)));
  glEnableVertexAttribArray(1);
  glBindVertexArray(0);
}