ljwglTexture.kt

import org.lwjgl.BufferUtils
import org.lwjgl.glfw.GLFW
import org.lwjgl.opengl.GL
import org.lwjgl.opengl.GL11
import org.lwjgl.system.MemoryUtil
import java.io.File
import javax.imageio.ImageIO

class TextureExample {
    private var window: Long = 0
    private var textureID = 0

    fun run() {
        init()
        val img = Res.getUri("drawable/img.png").toUri().path!!
        textureID = loadTexture(File(img))
        loop()

        GL11.glDeleteTextures(textureID)
        GLFW.glfwDestroyWindow(window)
        GLFW.glfwTerminate()
    }

    private fun init() {
        check(GLFW.glfwInit()) { "Unable to initialize GLFW" }

        window =
            GLFW.glfwCreateWindow(800, 600, "Texture Example", MemoryUtil.NULL, MemoryUtil.NULL)
        if (window == MemoryUtil.NULL) throw RuntimeException("Failed to create the GLFW window")

        GLFW.glfwMakeContextCurrent(window)
        GLFW.glfwShowWindow(window)
    }


    private fun loop() {
        while (!GLFW.glfwWindowShouldClose(window)) {
            GL11.glClear(GL11.GL_COLOR_BUFFER_BIT)

            GL11.glEnable(GL11.GL_TEXTURE_2D)
            GL11.glBindTexture(GL11.GL_TEXTURE_2D, textureID)

            GL11.glBegin(GL11.GL_QUADS)
            GL11.glTexCoord2f(0f, 0f)
            GL11.glVertex2f(-1f, -1f)
            GL11.glTexCoord2f(1f, 0f)
            GL11.glVertex2f(1f, -1f)
            GL11.glTexCoord2f(1f, 1f)
            GL11.glVertex2f(1f, 1f)
            GL11.glTexCoord2f(0f, 1f)
            GL11.glVertex2f(-1f, 1f)
            GL11.glEnd()

            GL11.glDisable(GL11.GL_TEXTURE_2D)

            GLFW.glfwSwapBuffers(window)
            GLFW.glfwPollEvents()
        }
    }


}

fun loadTexture(file: File): Int {
    val image = ImageIO.read(file)

    val width = image.width
    val height = image.height

    // Convert image to RGBA
    val pixels = IntArray(width * height)
    image.getRGB(0, 0, width, height, pixels, 0, width)

    val buffer = BufferUtils.createByteBuffer(width * height * 4)

    // OpenGL expects bottom-to-top, so flip vertically
    for (y in height - 1 downTo 0) {
        for (x in 0..<width) {
            val pixel = pixels[y * width + x]
            buffer.put(((pixel shr 16) and 0xFF).toByte()) // Red
            buffer.put(((pixel shr 8) and 0xFF).toByte()) // Green
            buffer.put((pixel and 0xFF).toByte()) // Blue
            buffer.put(((pixel shr 24) and 0xFF).toByte()) // Alpha
        }
    }

    buffer.flip()

    GL.createCapabilities()
    val textureID = GL11.glGenTextures()
    GL11.glBindTexture(GL11.GL_TEXTURE_2D, textureID)

    GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_WRAP_S, GL11.GL_CLAMP)
    GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_WRAP_T, GL11.GL_CLAMP)
    GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MIN_FILTER, GL11.GL_LINEAR)
    GL11.glTexParameteri(GL11.GL_TEXTURE_2D, GL11.GL_TEXTURE_MAG_FILTER, GL11.GL_LINEAR)

    GL11.glTexImage2D(
        GL11.GL_TEXTURE_2D,
        0,
        GL11.GL_RGBA8,
        width,
        height,
        0,
        GL11.GL_RGBA,
        GL11.GL_UNSIGNED_BYTE,
        buffer
    )

    return textureID
}

fun main(args: Array<String>) {
    TextureExample().run()
}