From e4a927982de51dacb602c667f888e6748a351fc5 Mon Sep 17 00:00:00 2001
From: Elias Naur <mail@eliasnaur.com>
Date: Sat, 22 Feb 2020 08:29:45 +0100
Subject: [PATCH] gpu: add Framebuffer.ReadPixels

Signed-off-by: Elias Naur <mail@eliasnaur.com>
---
 gpu/backend.go    |  1 +
 gpu/gl/backend.go | 10 ++++++++++
 gpu/gl/gl.go      |  1 +
 3 files changed, 12 insertions(+)

diff --git a/gpu/backend.go b/gpu/backend.go
index 88e30b9e..32000d1c 100644
--- a/gpu/backend.go
+++ b/gpu/backend.go
@@ -127,6 +127,7 @@ type Framebuffer interface {
 	Bind()
 	Invalidate()
 	Release()
+	ReadPixels(src image.Rectangle, pixels []byte) error
 }
 
 type Timer interface {
diff --git a/gpu/gl/backend.go b/gpu/gl/backend.go
index a5e38f27..033693fd 100644
--- a/gpu/gl/backend.go
+++ b/gpu/gl/backend.go
@@ -589,6 +589,16 @@ func (b *gpuBuffer) BindIndex() {
 	b.backend.funcs.BindBuffer(ELEMENT_ARRAY_BUFFER, b.obj)
 }
 
+func (f *gpuFramebuffer) ReadPixels(src image.Rectangle, pixels []byte) error {
+	glErr(f.funcs)
+	f.Bind()
+	if len(pixels) < src.Dx()*src.Dy() {
+		return errors.New("unexpected RGBA size")
+	}
+	f.funcs.ReadPixels(src.Min.X, src.Min.Y, src.Dx(), src.Dy(), RGBA, UNSIGNED_BYTE, pixels)
+	return glErr(f.funcs)
+}
+
 func (f *gpuFramebuffer) Bind() {
 	f.funcs.BindFramebuffer(FRAMEBUFFER, f.obj)
 }
diff --git a/gpu/gl/gl.go b/gpu/gl/gl.go
index 8dcb757f..41cb67eb 100644
--- a/gpu/gl/gl.go
+++ b/gpu/gl/gl.go
@@ -139,6 +139,7 @@ type Functions interface {
 	GetUniformLocation(p Program, name string) Uniform
 	InvalidateFramebuffer(target, attachment Enum)
 	LinkProgram(p Program)
+	ReadPixels(x, y, width, height int, format, ty Enum, data []byte)
 	RenderbufferStorage(target, internalformat Enum, width, height int)
 	ShaderSource(s Shader, src string)
 	TexImage2D(target Enum, level int, internalFormat int, width, height int, format, ty Enum, data []byte)