From 24e74750d5c31c510bc42b3295f3f618026e57bb Mon Sep 17 00:00:00 2001
From: Stephan Unverwerth <s.unverwerth@gmx.de>
Date: Mon, 24 May 2021 15:24:49 +0200
Subject: [PATCH] LibGL: Implement glReadBuffer()

---
 Userland/Libraries/LibGL/GL/gl.h              |  9 +++-
 Userland/Libraries/LibGL/GLContext.h          |  1 +
 Userland/Libraries/LibGL/GLUtils.cpp          |  5 +++
 .../Libraries/LibGL/SoftwareGLContext.cpp     | 41 +++++++++++++++++++
 Userland/Libraries/LibGL/SoftwareGLContext.h  |  6 ++-
 5 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibGL/GL/gl.h b/Userland/Libraries/LibGL/GL/gl.h
index 46408e70f64..b00383a57e6 100644
--- a/Userland/Libraries/LibGL/GL/gl.h
+++ b/Userland/Libraries/LibGL/GL/gl.h
@@ -73,9 +73,15 @@ extern "C" {
 #define GL_ONE_MINUS_DST_COLOR 0x0307
 #define GL_SRC_ALPHA_SATURATE 0x0308
 
-// Culled face side
+// Sides
+#define GL_FRONT_LEFT 0x0400
+#define GL_FRONT_RIGHT 0x0401
+#define GL_BACK_LEFT 0x0402
+#define GL_BACK_RIGHT 0x0403
 #define GL_FRONT 0x0404
 #define GL_BACK 0x0405
+#define GL_LEFT 0x0406
+#define GL_RIGHT 0x0407
 #define GL_FRONT_AND_BACK 0x0408
 
 // Error codes
@@ -204,6 +210,7 @@ GLAPI void glBlendFunc(GLenum sfactor, GLenum dfactor);
 GLAPI void glShadeModel(GLenum mode);
 GLAPI void glAlphaFunc(GLenum func, GLclampf ref);
 GLAPI void glHint(GLenum target, GLenum mode);
+GLAPI void glReadBuffer(GLenum mode);
 
 #ifdef __cplusplus
 }
diff --git a/Userland/Libraries/LibGL/GLContext.h b/Userland/Libraries/LibGL/GLContext.h
index 46b120610f3..c731540c818 100644
--- a/Userland/Libraries/LibGL/GLContext.h
+++ b/Userland/Libraries/LibGL/GLContext.h
@@ -53,6 +53,7 @@ public:
     virtual void gl_shade_model(GLenum mode) = 0;
     virtual void gl_alpha_func(GLenum func, GLclampf ref) = 0;
     virtual void gl_hint(GLenum target, GLenum mode) = 0;
+    virtual void gl_read_buffer(GLenum mode) = 0;
 
     virtual void present() = 0;
 };
diff --git a/Userland/Libraries/LibGL/GLUtils.cpp b/Userland/Libraries/LibGL/GLUtils.cpp
index d5f217862c1..539aacfb329 100644
--- a/Userland/Libraries/LibGL/GLUtils.cpp
+++ b/Userland/Libraries/LibGL/GLUtils.cpp
@@ -74,3 +74,8 @@ void glHint(GLenum target, GLenum mode)
 {
     g_gl_context->gl_hint(target, mode);
 }
+
+void glReadBuffer(GLenum mode)
+{
+    g_gl_context->gl_read_buffer(mode);
+}
\ No newline at end of file
diff --git a/Userland/Libraries/LibGL/SoftwareGLContext.cpp b/Userland/Libraries/LibGL/SoftwareGLContext.cpp
index 7c84dea98a8..a64d38b4270 100644
--- a/Userland/Libraries/LibGL/SoftwareGLContext.cpp
+++ b/Userland/Libraries/LibGL/SoftwareGLContext.cpp
@@ -1009,6 +1009,47 @@ void SoftwareGLContext::gl_hint(GLenum target, GLenum mode)
     // According to the spec implementors are free to ignore glHint. So we do.
 }
 
+void SoftwareGLContext::gl_read_buffer(GLenum mode)
+{
+    APPEND_TO_CALL_LIST_AND_RETURN_IF_NEEDED(gl_read_buffer, mode);
+
+    if (m_in_draw_state) {
+        m_error = GL_INVALID_OPERATION;
+        return;
+    }
+
+    // FIXME: Also allow aux buffers GL_AUX0 through GL_AUX3 here
+    // plus any aux buffer between 0 and GL_AUX_BUFFERS
+    if (mode != GL_FRONT_LEFT
+        && mode != GL_FRONT_RIGHT
+        && mode != GL_BACK_LEFT
+        && mode != GL_BACK_RIGHT
+        && mode != GL_FRONT
+        && mode != GL_BACK
+        && mode != GL_LEFT
+        && mode != GL_RIGHT) {
+        m_error = GL_INVALID_ENUM;
+        return;
+    }
+
+    // FIXME: We do not currently have aux buffers, so make it an invalid
+    // operation to select anything but front or back buffers. Also we do
+    // not allow selecting the stereoscopic RIGHT buffers since we do not
+    // have them configured.
+    if (mode != GL_FRONT_LEFT
+        && mode != GL_FRONT
+        && mode != GL_BACK_LEFT
+        && mode != GL_BACK
+        && mode != GL_FRONT
+        && mode != GL_BACK
+        && mode != GL_LEFT) {
+        m_error = GL_INVALID_OPERATION;
+        return;
+    }
+
+    m_current_read_buffer = mode;
+}
+
 void SoftwareGLContext::present()
 {
     m_rasterizer.blit_to(*m_frontbuffer);
diff --git a/Userland/Libraries/LibGL/SoftwareGLContext.h b/Userland/Libraries/LibGL/SoftwareGLContext.h
index 8ea205be08d..c368979365a 100644
--- a/Userland/Libraries/LibGL/SoftwareGLContext.h
+++ b/Userland/Libraries/LibGL/SoftwareGLContext.h
@@ -59,6 +59,7 @@ public:
     virtual void gl_shade_model(GLenum mode) override;
     virtual void gl_alpha_func(GLenum func, GLclampf ref) override;
     virtual void gl_hint(GLenum target, GLenum mode) override;
+    virtual void gl_read_buffer(GLenum mode) override;
 
     virtual void present() override;
 
@@ -117,6 +118,8 @@ private:
     GLenum m_alpha_test_func = GL_ALWAYS;
     GLclampf m_alpha_test_ref_value = 0;
 
+    GLenum m_current_read_buffer = GL_BACK;
+
     NonnullRefPtr<Gfx::Bitmap> m_frontbuffer;
 
     Clipper m_clipper;
@@ -172,7 +175,8 @@ private:
             decltype(&SoftwareGLContext::gl_blend_func),
             decltype(&SoftwareGLContext::gl_shade_model),
             decltype(&SoftwareGLContext::gl_alpha_func),
-            decltype(&SoftwareGLContext::gl_hint)>;
+            decltype(&SoftwareGLContext::gl_hint),
+            decltype(&SoftwareGLContext::gl_read_buffer)>;
 
         using ExtraSavedArguments = Variant<
             FloatMatrix4x4>;