From 2faf8a551d29c4c6714a4b89714511d0ba940a70 Mon Sep 17 00:00:00 2001
From: Zyko <13394516+Zyko0@users.noreply.github.com>
Date: Fri, 12 Apr 2024 19:19:17 +0200
Subject: [PATCH] Set max dst images to 8 + some wording

---
 examples/mrt/main.go        | 2 +-
 internal/atlas/image.go     | 2 +-
 internal/buffered/image.go  | 2 +-
 internal/graphics/vertex.go | 6 +++++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/examples/mrt/main.go b/examples/mrt/main.go
index 15c34d949..10e3e53a9 100644
--- a/examples/mrt/main.go
+++ b/examples/mrt/main.go
@@ -31,7 +31,7 @@ const (
 )
 
 var (
-	dsts = [4]*ebiten.Image{
+	dsts = [8]*ebiten.Image{
 		/*ebiten.NewImage(dstSize, dstSize),
 		ebiten.NewImage(dstSize, dstSize),
 		ebiten.NewImage(dstSize, dstSize),
diff --git a/internal/atlas/image.go b/internal/atlas/image.go
index 66e140fb6..d7915d577 100644
--- a/internal/atlas/image.go
+++ b/internal/atlas/image.go
@@ -590,7 +590,7 @@ func drawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.
 		// i and a source image might share the same atlas even though i != src.
 		for _, dst := range dsts {
 			if src != nil && dst != nil && dst.backend.image == src.backend.image {
-				panic("atlas: Image.DrawTriangles: source must be different from the receiver")
+				panic("atlas: DrawTrianglesMRT: source must be different from the destination images")
 			}
 		}
 	}
diff --git a/internal/buffered/image.go b/internal/buffered/image.go
index 185bee7bc..955e0fd51 100644
--- a/internal/buffered/image.go
+++ b/internal/buffered/image.go
@@ -218,7 +218,7 @@ func DrawTrianglesMRT(dsts [graphics.ShaderDstImageCount]*Image, srcs [graphics.
 				continue
 			}
 			if dst == src {
-				panic("buffered: DrawTrianglesMRT: source images must be different from the destination")
+				panic("buffered: DrawTrianglesMRT: source images must be different from the destination images")
 			}
 		}
 		if src != nil {
diff --git a/internal/graphics/vertex.go b/internal/graphics/vertex.go
index 02ba2e9fc..585e967aa 100644
--- a/internal/graphics/vertex.go
+++ b/internal/graphics/vertex.go
@@ -16,7 +16,11 @@ package graphics
 
 const (
 	ShaderSrcImageCount = 4
-	ShaderDstImageCount = 4
+	// The minimum guaranteed value for the number of target seems to be 8
+	// OpenGL(8): https://www.khronos.org/opengl/wiki/Framebuffer_Object#Framebuffer_Object_Structure
+	// DirectX11(8): https://learn.microsoft.com/en-us/windows/win32/direct3d11/d3d10-graphics-programming-guide-output-merger-stage#multiple-rendertargets-overview
+	// Metal(8): Page 7 of 15: https://developer.apple.com/metal/Metal-Feature-Set-Tables.pdf
+	ShaderDstImageCount = 8
 
 	// PreservedUniformVariablesCount represents the number of preserved uniform variables.
 	// Any shaders in Ebitengine must have these uniform variables.