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Custom Rendering

Document reviewed for 5.2.0
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While provided views are usually enough for most cases, some time people want to render their own views, or not rely on the view tree for rendering, and render everything manually. In those cases, it is possible to create custom views or render things manually directly drawing geometry, or by using a batcher or a shape builder.

Overriding a View

In the case you want a custom view where you can specify rendering code, you can use this template. You need to provide a renderInternal where you render things.

class MyCustomView : View() {
    override fun renderInternal(ctx: RenderContext) {
        // Custom Render Code here
        ctx.useBatcher { batcher ->
            batcher.drawQuad(ctx.getTex(Bitmaps.white), x = 0f, y = 0f, width = 100f, height = 100f, m = globalMatrix, filtering = false, colorMul = Colors.RED, blendMode = renderBlendMode, program = null)
        ctx.useLineBatcher { 
            it.line(Point(0, 0), Point(100, 100), Colors.RED, m = globalMatrix)
    override fun getLocalBoundsInternal(): Rectangle {
        return Rectangle(0, 0, 100, 100)

RenderableView to create a view for custom rendering

Since KorGE requires at least one view to work, you can use this predefined view that only requires a callback to start rendering. For example:

fun main() = Korge {
    renderableView(Size(100, 100)) {
        ctx.useBatcher {
            // ...
        ctx.useLineBatcher {
            // ...
        // Or using RenderContext2D
        ctx2d.drawText("Hello", DefaultTtfFontAsBitmap)
        ctx2d.simplePath(buildVectorPath { 
            circle(Point(0, 0), 100f)


BatchBuilder2D is designed to buffer geometry, typically quads, to later emit a command to the GPU to render all the geometries at once. With a RenderContext that is provided to the render function, you can call:

ctx.useBatcher { batcher ->
    // Your code here...

Methods here require a Texture or TextureCoords.

Getting textures from Bitmap or BitmapSlice/BmpSlice

Bitmap are pixels stored typically on the CPU. But the GPU requires textures. KorGE provides a managed way to use textures. In the rendering code, you can get a managed Texture auto GCed texture by calling the getTex(bitmap) method like:

val texture: Texture = ctx.getTex(bitmap)
val textureCoords: TextureCoords = ctx.getTex(bitmapSlice)

Rendering a solid rect square

We need a white texture, and then we tint it. We provide the globalMatrix of our view, so all the transformations are taken into account, and use the default program for rendering (vertex + fragment). To get a white texture, we use Bitmaps.white: BmpSlice and convert it into a TextureCoords:

ctx.useBatcher { batcher ->
    batcher.drawQuad(ctx.getTex(Bitmaps.white), x = 0f, y = 0f, width = 100f, height = 100f, m = globalMatrix, filtering = false, colorMul = Colors.RED, blendMode = renderBlendMode, program = null)

Render a full TexturedVertexArray

If we want to precompute a set of vertices and later render them, we can use a TexturedVertexArray and the drawVertices method:

ctx.useBatcher {
        TexturedVertexArray.fromPointArrayList(pointArrayListOf(Point(0, 0), Point(100, 0), Point(100, 100)), Colors.RED),


If we need a higher level API supporting local transformations, vector rendering, etc. we can use RenderContext2D, it is like a Context2D but a bit simpler and more limited. Also, this API is not anti-aliased. For that, you can check the Graphics view.

View.renderCtx2d sets the view matrix, blending mode, size, multiplication color, etc.

view.renderCtx2d(ctx) {
    keep {
        translate(100.0, 100.0)
        drawText("Hello World", DefaultTtfFontAsBitmap)
        simplePath(buildVectorPath { 
             circle(Point(0, 0), 100f)
        }, Colors.RED)

When using a RenderableView that already sets everything, you can just use this.ctx2d.


AG provides the lowest possible interface for rendering. It supports rendering geometry by providing vertices with attributes, indices, shader programs, etc. Since this is a complex API it is discouraged for most cases, and only if you know what you are doing. You can search for AG.draw calls in the code to figure out how it the API is used.

val frameBuffer = ctx.currentFrameBufferOrMain,, vertexData = ...)

Custom Rendering full example

Here you can find a full example doing custom rendering, using both the batcher, render context2d, textures, etc.:

import korlibs.image.color.*
import korlibs.image.font.*
import korlibs.image.format.*
import korlibs.korge.*
import korlibs.korge.render.*
import korlibs.korge.scene.*
import korlibs.korge.view.*
import korlibs.math.geom.*

suspend fun main() = Korge(windowSize = Size(512, 512), backgroundColor = Colors["#2b2b2b"]) {
    val sceneContainer = sceneContainer()

    sceneContainer.changeTo({ MyScene() })

class MyScene : Scene() {
    override suspend fun SContainer.sceneMain() {
        val img = resourcesVfs["korge.png"].readBitmapSlice()
        var mx = 0f
        addUpdater {
        renderableView {
            // Rendering code here:
            val texs = ctx.agBitmapTextureManager

            // Batcher:
            ctx.useBatcher {

            // Drawer:
            ctx2d.imageScale(texs.getTexture(img), 200.0, 200.0)
            ctx2d.drawText("hello world", DefaultTtfFontAsBitmap)
            ctx2d.ellipse(Point(200 + mx, 200), Size(120, 70), Colors.RED)
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