From c5c93d94426746cde675fbf2551d6981c0a7f294 Mon Sep 17 00:00:00 2001
From: faiface <faiface@ksp.sk>
Date: Wed, 23 Nov 2016 18:06:55 +0100
Subject: [PATCH] add error handling

---
 pixelgl/error.go   | 41 +++++++++++++++++++++++++++++++++++++++++
 pixelgl/texture.go | 18 ++++++++++++++----
 pixelgl/thread.go  |  1 +
 pixelgl/vertex.go  | 25 +++++++++++++++++++------
 4 files changed, 75 insertions(+), 10 deletions(-)
 create mode 100644 pixelgl/error.go

diff --git a/pixelgl/error.go b/pixelgl/error.go
new file mode 100644
index 0000000..9077856
--- /dev/null
+++ b/pixelgl/error.go
@@ -0,0 +1,41 @@
+package pixelgl
+
+import (
+	"github.com/go-gl/gl/v3.3-core/gl"
+	"github.com/pkg/errors"
+)
+
+// GetLastError returns (and consumes) the last error generated by OpenGL.
+// If no error has been generated, this function returns nil.
+//
+// Call this function only inside the OpenGL thread (Do, DoErr or DoVal function). It's not guaranteed
+// to work correctly outside of it, because the thread swallows extra unchecked errors.
+func GetLastError() error {
+	err := uint32(gl.NO_ERROR)
+	for e := gl.GetError(); e != gl.NO_ERROR; e = gl.GetError() {
+		err = e
+	}
+	if err == gl.NO_ERROR {
+		return nil
+	}
+	switch err {
+	case gl.INVALID_ENUM:
+		return errors.New("invalid enum")
+	case gl.INVALID_VALUE:
+		return errors.New("invalid value")
+	case gl.INVALID_OPERATION:
+		return errors.New("invalid operation")
+	case gl.STACK_OVERFLOW:
+		return errors.New("stack overflow")
+	case gl.STACK_UNDERFLOW:
+		return errors.New("stack underflow")
+	case gl.OUT_OF_MEMORY:
+		return errors.New("out of memory")
+	case gl.INVALID_FRAMEBUFFER_OPERATION:
+		return errors.New("invalid framebuffer operation")
+	case gl.CONTEXT_LOST:
+		return errors.New("context lost")
+	default:
+		return errors.New("unknown error")
+	}
+}
diff --git a/pixelgl/texture.go b/pixelgl/texture.go
index e56395b..06211f9 100644
--- a/pixelgl/texture.go
+++ b/pixelgl/texture.go
@@ -1,6 +1,9 @@
 package pixelgl
 
-import "github.com/go-gl/gl/v3.3-core/gl"
+import (
+	"github.com/go-gl/gl/v3.3-core/gl"
+	"github.com/pkg/errors"
+)
 
 // Texture is an OpenGL texture.
 type Texture struct {
@@ -10,11 +13,12 @@ type Texture struct {
 
 // NewTexture creates a new texture with the specified width and height.
 // The pixels must be a sequence of RGBA values.
-func NewTexture(parent BeginEnder, width, height int, pixels []uint8) *Texture {
+func NewTexture(parent BeginEnder, width, height int, pixels []uint8) (*Texture, error) {
 	texture := &Texture{parent: parent}
-	Do(func() {
+	err := DoErr(func() error {
 		gl.GenTextures(1, &texture.tex)
 		gl.BindTexture(gl.TEXTURE_2D, texture.tex)
+
 		gl.TexImage2D(
 			gl.TEXTURE_2D,
 			0,
@@ -27,9 +31,15 @@ func NewTexture(parent BeginEnder, width, height int, pixels []uint8) *Texture {
 			gl.Ptr(pixels),
 		)
 		gl.GenerateMipmap(gl.TEXTURE_2D)
+
 		gl.BindTexture(gl.TEXTURE_2D, 0)
+
+		return GetLastError()
 	})
-	return texture
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create a texture")
+	}
+	return texture, nil
 }
 
 // Begin binds a texture.
diff --git a/pixelgl/thread.go b/pixelgl/thread.go
index ffb2a61..555faef 100644
--- a/pixelgl/thread.go
+++ b/pixelgl/thread.go
@@ -16,6 +16,7 @@ func init() {
 	go func() {
 		runtime.LockOSThread()
 		for f := range callQueue {
+			GetLastError() // swallow unchecked errors
 			f()
 		}
 	}()
diff --git a/pixelgl/vertex.go b/pixelgl/vertex.go
index 836df5b..d46919a 100644
--- a/pixelgl/vertex.go
+++ b/pixelgl/vertex.go
@@ -1,6 +1,9 @@
 package pixelgl
 
-import "github.com/go-gl/gl/v3.3-core/gl"
+import (
+	"github.com/go-gl/gl/v3.3-core/gl"
+	"github.com/pkg/errors"
+)
 
 // VertexFormat defines a data format in a vertex buffer.
 //
@@ -96,13 +99,13 @@ type VertexArray struct {
 }
 
 // NewVertexArray creates a new vertex array and wraps another BeginEnder around it.
-func NewVertexArray(parent BeginEnder, format VertexFormat, mode VertexDrawMode, usage VertexUsage, data []float64) *VertexArray {
+func NewVertexArray(parent BeginEnder, format VertexFormat, mode VertexDrawMode, usage VertexUsage, data []float64) (*VertexArray, error) {
 	va := &VertexArray{
 		parent: parent,
 		format: format,
 		mode:   mode,
 	}
-	Do(func() {
+	err := DoErr(func() error {
 		gl.GenVertexArrays(1, &va.vao)
 		gl.BindVertexArray(va.vao)
 
@@ -129,8 +132,13 @@ func NewVertexArray(parent BeginEnder, format VertexFormat, mode VertexDrawMode,
 
 		gl.BindBuffer(gl.ARRAY_BUFFER, 0)
 		gl.BindVertexArray(0)
+
+		return GetLastError()
 	})
-	return va
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to create a vertex array")
+	}
+	return va, nil
 }
 
 // VertexFormat returns the format of the vertices inside a vertex array.
@@ -164,12 +172,17 @@ func (va *VertexArray) Draw() {
 // UpdateData overwrites the current vertex array data starting at the index offset.
 //
 // Offset is not a number of bytes, instead, it's an index in the array.
-func (va *VertexArray) UpdateData(offset int, data []float64) {
-	Do(func() {
+func (va *VertexArray) UpdateData(offset int, data []float64) error {
+	err := DoErr(func() error {
 		gl.BindBuffer(gl.ARRAY_BUFFER, va.vbo)
 		gl.BufferSubData(gl.ARRAY_BUFFER, 8*offset, 8*len(data), gl.Ptr(data))
 		gl.BindBuffer(gl.ARRAY_BUFFER, 0)
+		return GetLastError()
 	})
+	if err != nil {
+		return errors.Wrap(err, "failed to update vertex array")
+	}
+	return nil
 }
 
 // Begin binds a vertex array and it's associated vertex buffer.