ocelot-desktop/src/main/scala/ocelot/desktop/graphics/ShaderProgram.scala

package ocelot.desktop.graphics

import ocelot.desktop.geometry.Transform2D
import ocelot.desktop.util.{Resource, ResourceManager}
import org.apache.logging.log4j.scala.Logging
import org.lwjgl.opengl.GL20

import scala.io.Source

class ShaderProgram(name: String) extends Logging with Resource {
  logger.info(s"Loading shader program ($name)")

  val fragmentShader: Int = createShader(Source.fromResource(s"ocelot/desktop/shader/$name.frag", getClass.getClassLoader), GL20.GL_FRAGMENT_SHADER, "fragment")
  val vertexShader: Int = createShader(Source.fromResource(s"ocelot/desktop/shader/$name.vert", getClass.getClassLoader), GL20.GL_VERTEX_SHADER, "vertex")

  val shaderProgram: Int = GL20.glCreateProgram()

  GL20.glAttachShader(shaderProgram, vertexShader)
  GL20.glAttachShader(shaderProgram, fragmentShader)
  GL20.glLinkProgram(shaderProgram)

  {
    val success = Array(0)
    GL20.glGetProgramiv(shaderProgram, GL20.GL_LINK_STATUS, success)

    if (success.head == 0) {
      val info = GL20.glGetProgramInfoLog(shaderProgram)
      logger.error(s"Failed to link shader program ($name)\n$info")
      throw new RuntimeException("Shader linkage failed")
    }
  }

  ResourceManager.registerResource(this)

  def freeResource(): Unit = {
    logger.debug(s"Destroyed shader program ($name)")
    GL20.glDeleteProgram(shaderProgram)
    GL20.glDeleteShader(vertexShader)
    GL20.glDeleteShader(fragmentShader)
  }

  def bind(): Unit = {
    GL20.glUseProgram(shaderProgram)
  }

  def set(name: String, transform: Transform2D): Unit = {
    bind()

    val array = transform.array ++ Array(0f, 0f, 1f)
    GL20.glUniformMatrix3fv(getLocation(name), true, array)
  }

  def set(name: String, v: Int): Unit = {
    bind()
    GL20.glUniform1i(getLocation(name), v)
  }

  private def getLocation(name: String): Int = {
    GL20.glGetUniformLocation(shaderProgram, name)
  }

  private def createShader(source: Source, ty: Int, s: String): Int = {
    val shader = GL20.glCreateShader(ty)

    GL20.glShaderSource(shader, source.mkString)
    GL20.glCompileShader(shader)

    val success = Array(0)
    GL20.glGetShaderiv(shader, GL20.GL_COMPILE_STATUS, success)

    if (success.head == 0) {
      val info = GL20.glGetShaderInfoLog(shader)
      logger.error(s"Failed to compile shader ($s)\n$info")
      throw new RuntimeException("Shader compilation failed")
    }

    source.close()

    shader
  }
}