Update FrameBuffer to handle multiple color attachments

core/src/androidMain/kotlin/com/lehaine/littlekt/AndroidGL.kt

@@ -45,6 +45,29 @@ class AndroidGL(private val engineStats: EngineStats) : GL {
         GLES20.glClearStencil(stencil)
     }
 
+    override fun clearBufferiv(buffer: Int, drawBuffer: Int, value: IntBuffer) {
+        engineStats.calls++
+        value as IntBufferImpl
+        GLES30.glClearBufferiv(buffer, drawBuffer, value.buffer)
+    }
+
+    override fun clearBufferuiv(buffer: Int, drawBuffer: Int, value: IntBuffer) {
+        engineStats.calls++
+        value as IntBufferImpl
+        GLES30.glClearBufferuiv(buffer, drawBuffer, value.buffer)
+    }
+
+    override fun clearBufferfv(buffer: Int, drawBuffer: Int, value: FloatBuffer) {
+        engineStats.calls++
+        value as FloatBufferImpl
+        GLES30.glClearBufferfv(buffer, drawBuffer, value.buffer)
+    }
+
+    override fun clearBufferfi(buffer: Int, drawBuffer: Int, depth: Float, stencil: Int) {
+        engineStats.calls++
+        GLES30.glClearBufferfi(buffer, drawBuffer, depth, stencil)
+    }
+
     override fun colorMask(red: Boolean, green: Boolean, blue: Boolean, alpha: Boolean) {
         engineStats.calls++
         GLES20.glColorMask(red, green, blue, alpha)
@@ -660,6 +683,12 @@ class AndroidGL(private val engineStats: EngineStats) : GL {
         GLES20.glDrawElements(mode, count, type, offset)
     }
 
+    override fun drawBuffers(size: Int, buffers: IntBuffer) {
+        engineStats.calls++
+        buffers as IntBufferImpl
+        GLES30.glDrawBuffers(size, buffers.buffer)
+    }
+
     override fun pixelStorei(pname: Int, param: Int) {
         engineStats.calls++
         GLES20.glPixelStorei(pname, param)

core/src/commonMain/kotlin/com/lehaine/littlekt/graph/node/FrameBufferNode.kt

@@ -4,7 +4,10 @@ import com.lehaine.littlekt.graph.SceneGraph
 import com.lehaine.littlekt.graph.node.annotation.SceneGraphDslMarker
 import com.lehaine.littlekt.graph.node.resource.InputEvent
 import com.lehaine.littlekt.graph.node.ui.Control
-import com.lehaine.littlekt.graphics.*
+import com.lehaine.littlekt.graphics.Camera
+import com.lehaine.littlekt.graphics.Color
+import com.lehaine.littlekt.graphics.FrameBuffer
+import com.lehaine.littlekt.graphics.Texture
 import com.lehaine.littlekt.graphics.g2d.Batch
 import com.lehaine.littlekt.graphics.g2d.shape.ShapeRenderer
 import com.lehaine.littlekt.graphics.gl.ClearBufferMask
@@ -49,7 +52,7 @@ open class FrameBufferNode : CanvasLayer() {
     /**
      * The color buffer texture from the [FrameBuffer].
      */
-    val fboTexture: Texture? get() = fbo?.colorBufferTexture
+    val fboTexture: Texture? get() = fbo?.textures?.getOrNull(0)
 
     /**
      * Signal that is emitted when the [FrameBuffer] is resized and recreated.
@@ -98,8 +101,12 @@ open class FrameBufferNode : CanvasLayer() {
             fbo = FrameBuffer(
                 width,
                 height,
-                minFilter = TexMinFilter.NEAREST,
-                magFilter = TexMagFilter.NEAREST
+                colorAttachments = listOf(
+                    FrameBuffer.ColorAttachment(
+                        minFilter = TexMinFilter.NEAREST,
+                        magFilter = TexMagFilter.NEAREST
+                    )
+                ),
             ).also { it.prepare(scene.context) }
             viewport.width = width
             viewport.height = height

core/src/commonMain/kotlin/com/lehaine/littlekt/graphics/FrameBuffer.kt

@@ -3,6 +3,7 @@ package com.lehaine.littlekt.graphics
 import com.lehaine.littlekt.Context
 import com.lehaine.littlekt.Disposable
 import com.lehaine.littlekt.file.createIntBuffer
+import com.lehaine.littlekt.graphics.FrameBuffer.ColorAttachment
 import com.lehaine.littlekt.graphics.gl.*
 import com.lehaine.littlekt.math.MutableVec4i
 import kotlin.contracts.ExperimentalContracts
@@ -13,23 +14,67 @@ import kotlin.contracts.contract
  * Encapsulates OpenGL frame buffer objects.
  * @param width the width of the framebuffer in pixels
  * @param height the height of the framebuffer in pixels
+ * @param colorAttachments the list of [ColorAttachment] to attach to the FrameBuffer.
  * @param hasDepth whether to attach a depth buffer. Defaults to false.
  * @param hasStencil whether to attach a stencil buffer. Defaults to false.
- * @param format the format of the color buffer
+ * @param hasPackedDepthStencil whether to attach a packed depth/stencil buffer. Defaults to false.
  * @author Colton Daily
  * @date 11/25/2021
  */
 open class FrameBuffer(
     val width: Int,
     val height: Int,
+    val colorAttachments: List<ColorAttachment> = listOf(ColorAttachment()),
     val hasDepth: Boolean = false,
     val hasStencil: Boolean = false,
     var hasPackedDepthStencil: Boolean = false,
-    val format: Pixmap.Format = Pixmap.Format.RGBA8888,
-    val minFilter: TexMinFilter = TexMinFilter.LINEAR,
-    val magFilter: TexMagFilter = TexMagFilter.LINEAR,
 ) : Preparable, Disposable {
 
+    /**
+     * Encapsulates OpenGL frame buffer objects.
+     * @param width the width of the framebuffer in pixels
+     * @param height the height of the framebuffer in pixels
+     * @param format format of the color buffer
+     * @param hasDepth whether to attach a depth buffer. Defaults to false.
+     * @param hasStencil whether to attach a stencil buffer. Defaults to false.
+     * @param hasPackedDepthStencil whether to attach a packed depth/stencil buffer. Defaults to false.
+     * @param minFilter texture min filter
+     * @param magFilter texture mag filter
+     * @param wrap format for UV texture wrap
+     */
+    constructor(
+        width: Int,
+        height: Int,
+        hasDepth: Boolean = false,
+        hasStencil: Boolean = false,
+        hasPackedDepthStencil: Boolean = false,
+        format: Pixmap.Format = Pixmap.Format.RGBA8888,
+        minFilter: TexMinFilter = TexMinFilter.LINEAR,
+        magFilter: TexMagFilter = TexMagFilter.LINEAR,
+        wrap: TexWrap = TexWrap.CLAMP_TO_EDGE,
+    ) : this(
+        width,
+        height,
+        listOf(ColorAttachment(format, minFilter, magFilter, wrap)),
+        hasDepth,
+        hasStencil,
+        hasPackedDepthStencil
+    )
+
+    /**
+     * A color attachment to be used in [FrameBuffer].
+     * @param format format of the color buffer
+     * @param minFilter texture min filter
+     * @param magFilter texture mag filter
+     * @param wrap format for UV texture wrap
+     */
+    class ColorAttachment(
+        val format: Pixmap.Format = Pixmap.Format.RGBA8888,
+        val minFilter: TexMinFilter = TexMinFilter.LINEAR,
+        val magFilter: TexMagFilter = TexMagFilter.LINEAR,
+        val wrap: TexWrap = TexWrap.CLAMP_TO_EDGE,
+    )
+
     /**
      * Gets set when the frame buffer is prepared by the application
      */
@@ -45,8 +90,18 @@ open class FrameBuffer(
     private var isBound = false
     private var isPrepared = false
 
-    var texture: Texture? = null
-    val colorBufferTexture get() = texture!!
+    private val _textures = mutableListOf<Texture>()
+    val textures: List<Texture> get() = _textures
+
+    /**
+     * Alias for `textures.getOrNull(0)`.
+     */
+    val texture: Texture? get() = textures.getOrNull(0)
+
+    /**
+     * Alias for `textures[0]`.
+     */
+    val colorBufferTexture: Texture get() = textures[0]
 
     override val prepared: Boolean
         get() = isPrepared
@@ -81,15 +136,31 @@ open class FrameBuffer(
                 gl.renderBufferStorage(RenderBufferInternalFormat.DEPTH24_STENCIL8, width, height)
             }
         }
-        texture = Texture(GLTextureData(width, height, 0, format.glFormat, format.glFormat, format.glType)).apply {
-            minFilter = this@FrameBuffer.minFilter
-            magFilter = this@FrameBuffer.magFilter
-            uWrap = TexWrap.CLAMP_TO_EDGE
-            vWrap = TexWrap.CLAMP_TO_EDGE
-        }.also { it.prepare(context) } // preparing the texture will also bind it
 
-        texture?.glTexture?.let {
-            gl.frameBufferTexture2D(FrameBufferRenderBufferAttachment.COLOR_ATTACHMENT(), it, 0)
+        colorAttachments.forEachIndexed { i, colorAttachment ->
+            _textures += Texture(
+                GLTextureData(
+                    width,
+                    height,
+                    0,
+                    colorAttachment.format.glFormat,
+                    colorAttachment.format.glFormat,
+                    colorAttachment.format.glType
+                )
+            ).apply {
+                minFilter = colorAttachment.minFilter
+                magFilter = colorAttachment.magFilter
+                uWrap = colorAttachment.wrap
+                vWrap = colorAttachment.wrap
+            }.also { texture ->
+                texture.prepare(context) // preparing the texture will also bind it
+                gl.frameBufferTexture2D(
+                    FrameBufferRenderBufferAttachment.COLOR_ATTACHMENT(i),
+                    texture.glTexture
+                        ?: throw RuntimeException("FrameBuffer failed on attempting to add color attachment($i)!"),
+                    0
+                )
+            }
         }
 
         depthBufferHandle?.let {
@@ -104,9 +175,6 @@ open class FrameBuffer(
         }
 
         gl.bindDefaultRenderBuffer()
-        texture?.glTexture?.let {
-            gl.bindTexture(TextureTarget._2D, it)
-        }
 
         var result = gl.checkFrameBufferStatus()
         if (result == FrameBufferStatus.FRAMEBUFFER_UNSUPPORTED && hasDepth && hasStencil &&
@@ -190,7 +258,9 @@ open class FrameBuffer(
     }
 
     override fun dispose() {
-        texture?.dispose()
+        _textures.forEach {
+            it.dispose()
+        }
 
         if (hasDepth) {
             depthBufferHandle?.let {

core/src/commonMain/kotlin/com/lehaine/littlekt/graphics/GL.kt

@@ -63,6 +63,10 @@ interface GL {
     fun clear(mask: ClearBufferMask) = clear(mask.glFlag)
     fun clearDepth(depth: Float)
     fun clearStencil(stencil: Int)
+    fun clearBufferiv(buffer: Int, drawBuffer: Int, value: IntBuffer)
+    fun clearBufferuiv(buffer: Int, drawBuffer: Int, value: IntBuffer)
+    fun clearBufferfv(buffer: Int, drawBuffer: Int, value: FloatBuffer)
+    fun clearBufferfi(buffer: Int, drawBuffer: Int, depth: Float, stencil: Int)
     fun colorMask(red: Boolean, green: Boolean, blue: Boolean, alpha: Boolean)
     fun cullFace(mode: Int)
     fun cullFace(mode: CullFaceMode) = cullFace(mode.glFlag)
@@ -232,26 +236,29 @@ interface GL {
 
     fun uniform1fv(uniformLocation: UniformLocation, floats: FloatArray)
     fun uniform1fv(uniformLocation: UniformLocation, floats: Array<Float>) =
-        uniform1fv(uniformLocation, floats.toFloatArray())
+        uniform1fv(uniformLocation, floats.toFloatArray()) // TODO optimize this so it doesn't create a new array
 
     fun uniform2fv(uniformLocation: UniformLocation, floats: FloatArray)
     fun uniform2fv(uniformLocation: UniformLocation, floats: Array<Float>) =
-        uniform2fv(uniformLocation, floats.toFloatArray())
+        uniform2fv(uniformLocation, floats.toFloatArray()) // TODO optimize this so it doesn't create a new array
 
     fun uniform3fv(uniformLocation: UniformLocation, floats: FloatArray)
     fun uniform3fv(uniformLocation: UniformLocation, floats: Array<Float>) =
-        uniform3fv(uniformLocation, floats.toFloatArray())
+        uniform3fv(uniformLocation, floats.toFloatArray()) // TODO optimize this so it doesn't create a new array
 
     fun uniform4fv(uniformLocation: UniformLocation, floats: FloatArray)
     fun uniform4fv(uniformLocation: UniformLocation, floats: Array<Float>) =
-        uniform4fv(uniformLocation, floats.toFloatArray())
+        uniform4fv(uniformLocation, floats.toFloatArray()) // TODO optimize this so it doesn't create a new array
 
     fun drawArrays(mode: Int, offset: Int, count: Int)
     fun drawArrays(mode: DrawMode, offset: Int, count: Int) = drawArrays(mode.glFlag, offset, count)
     fun drawElements(mode: Int, count: Int, type: Int, offset: Int)
     fun drawElements(mode: DrawMode, count: Int, type: IndexType, offset: Int) =
         drawElements(mode.glFlag, count, type.glFlag, offset)
 
+    fun drawBuffers(size: Int, buffers: IntBuffer)
+    fun drawBuffers(buffers: IntBuffer) = drawBuffers(buffers.limit, buffers)
+
     fun pixelStorei(pname: Int, param: Int)
     fun pixelStorei(pname: PixelStoreParameter, param: Int) = pixelStorei(pname.glFlag, param)
 

core/src/commonMain/kotlin/com/lehaine/littlekt/graphics/g2d/font/VectorFont.kt

@@ -63,7 +63,7 @@ class VectorFont(private val font: TtfFont) : Preparable {
             context.graphics.width,
             context.graphics.height,
         ).apply { prepare(context) }
-        fboSlice = fbo.colorBufferTexture.slice()
+        fboSlice = fbo.textures[0].slice()
         isPrepared = true
     }
 
@@ -76,7 +76,7 @@ class VectorFont(private val font: TtfFont) : Preparable {
         fbo = FrameBuffer(
             width, height
         ).apply { prepare(context) }
-        fboSlice = fbo.colorBufferTexture.slice()
+        fboSlice = fbo.textures[0].slice()
     }
 
     /**

core/src/commonMain/kotlin/com/lehaine/littlekt/graphics/shader/Shader.kt

@@ -25,6 +25,7 @@ abstract class FragmentShaderModel : GlslGenerator(), FragmentShader {
 
     var gl_FragCoord by BuiltinVarDelegate()
     var gl_FragColor by BuiltinVarDelegate()
+    val gl_FragData by BuiltInVec4ArrayDelegate()
 
     val gl_FrontFacing = "gl_FrontFacing".bool
 
@@ -67,9 +68,7 @@ abstract class FragmentShaderModel : GlslGenerator(), FragmentShader {
 
         other as FragmentShaderModel
 
-        if (source != other.source) return false
-
-        return true
+        return source == other.source
     }
 
     override fun hashCode(): Int {