LibGL: Implement glGetError and underlying function

This implements `glGetError` and correctly sets the state machine's
error macro (similar to LibC `errno`) when an invalid operation is
performed. This is reset on completion of a successful operation.

Userland/Libraries/LibGL/GL/gl.h

@@ -37,6 +37,14 @@ extern "C" {
 #define GL_RENDERER 0x1F01
 #define GL_VERSION 0x1F02
 
+// Error codes
+#define GL_NO_ERROR 0
+#define GL_INVALID_ENUM 0x500
+#define GL_INVALID_VALUE 0x501
+#define GL_INVALID_OPERATION 0x502
+#define GL_INVALID_FRAMEBUFFER_OPERATION 0x503
+#define GL_OUT_OF_MEMORY 0x504
+
 //
 // OpenGL typedefs
 //
@@ -66,6 +74,7 @@ GLAPI void glClearColor(GLclampf red, GLclampf green, GLclampf blue, GLclampf al
 GLAPI void glColor3f(GLfloat r, GLfloat g, GLfloat b);
 GLAPI void glEnd();
 GLAPI void glFrustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble nearVal, GLdouble farVal);
+GLAPI GLenum glGetError();
 GLAPI GLubyte* glGetString(GLenum name);
 GLAPI void glLoadIdentity();
 GLAPI void glMatrixMode(GLenum mode);

Userland/Libraries/LibGL/GLContext.h

@@ -22,6 +22,7 @@ public:
     virtual void gl_color(GLdouble r, GLdouble g, GLdouble b, GLdouble a) = 0;
     virtual void gl_end() = 0;
     virtual void gl_frustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near_val, GLdouble far_val) = 0;
+    virtual GLenum gl_get_error() = 0;
     virtual GLubyte* gl_get_string(GLenum name) = 0;
     virtual void gl_load_identity() = 0;
     virtual void gl_matrix_mode(GLenum mode) = 0;

Userland/Libraries/LibGL/GLUtils.cpp

@@ -29,3 +29,8 @@ void glViewport(GLint x, GLint y, GLsizei width, GLsizei height)
 {
     g_gl_context->gl_viewport(x, y, width, height);
 }
+
+GLenum glGetError()
+{
+    return g_gl_context->gl_get_error();
+}

Userland/Libraries/LibGL/SoftwareGLContext.cpp

@@ -129,7 +129,13 @@ static void clip_triangle_against_frustum(Vector<FloatVector4>& in_vec)
 
 void SoftwareGLContext::gl_begin(GLenum mode)
 {
+    if (mode < GL_TRIANGLES || mode > GL_POLYGON) {
+        m_error = GL_INVALID_ENUM;
+        return;
+    }
+
     m_current_draw_mode = mode;
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_clear(GLbitfield mask)
@@ -141,19 +147,22 @@ void SoftwareGLContext::gl_clear(GLbitfield mask)
 
         uint64_t color = r << 16 | g << 8 | b;
         (void)(color);
+        m_error = GL_NO_ERROR;
     } else {
-        // set gl error here!?
+        m_error = GL_INVALID_ENUM;
     }
 }
 
 void SoftwareGLContext::gl_clear_color(GLclampf red, GLclampf green, GLclampf blue, GLclampf alpha)
 {
     m_clear_color = { red, green, blue, alpha };
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_color(GLdouble r, GLdouble g, GLdouble b, GLdouble a)
 {
     m_current_vertex_color = { (float)r, (float)g, (float)b, (float)a };
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_end()
@@ -218,7 +227,8 @@ void SoftwareGLContext::gl_end()
             triangle_list.append(triangle);
         }
     } else {
-        VERIFY_NOT_REACHED();
+        m_error = GL_INVALID_ENUM;
+        return;
     }
 
     // Now let's transform each triangle and send that to the GPU
@@ -374,6 +384,8 @@ void SoftwareGLContext::gl_end()
     triangle_list.clear();
     processed_triangles.clear();
     vertex_list.clear();
+
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_frustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near_val, GLdouble far_val)
@@ -398,6 +410,13 @@ void SoftwareGLContext::gl_frustum(GLdouble left, GLdouble right, GLdouble botto
         dbgln_if(GL_DEBUG, "glFrustum(): frustum created with curr_matrix_mode == GL_MODELVIEW!!!");
         m_projection_matrix = m_model_view_matrix * frustum;
     }
+
+    m_error = GL_NO_ERROR;
+}
+
+GLenum SoftwareGLContext::gl_get_error()
+{
+    return m_error;
 }
 
 GLubyte* SoftwareGLContext::gl_get_string(GLenum name)
@@ -414,7 +433,7 @@ GLubyte* SoftwareGLContext::gl_get_string(GLenum name)
         break;
     }
 
-    // FIXME: Set glError to GL_INVALID_ENUM here
+    m_error = GL_INVALID_ENUM;
     return nullptr;
 }
 
@@ -426,12 +445,19 @@ void SoftwareGLContext::gl_load_identity()
         m_model_view_matrix = FloatMatrix4x4::identity();
     else
         VERIFY_NOT_REACHED();
+
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_matrix_mode(GLenum mode)
 {
-    VERIFY(mode == GL_MODELVIEW || mode == GL_PROJECTION);
+    if (mode < GL_MODELVIEW || mode > GL_PROJECTION) {
+        m_error = GL_INVALID_ENUM;
+        return;
+    }
+
     m_current_matrix_mode = mode;
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_push_matrix()
@@ -449,6 +475,8 @@ void SoftwareGLContext::gl_push_matrix()
         dbgln_if(GL_DEBUG, "glPushMatrix(): Attempt to push matrix with invalid matrix mode {})", m_current_matrix_mode);
         return;
     }
+
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_pop_matrix()
@@ -467,6 +495,8 @@ void SoftwareGLContext::gl_pop_matrix()
         dbgln_if(GL_DEBUG, "glPopMatrix(): Attempt to pop matrix with invalid matrix mode, {}", m_current_matrix_mode);
         return;
     }
+
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_rotate(GLdouble angle, GLdouble x, GLdouble y, GLdouble z)
@@ -479,6 +509,8 @@ void SoftwareGLContext::gl_rotate(GLdouble angle, GLdouble x, GLdouble y, GLdoub
         m_model_view_matrix = m_model_view_matrix * rotation_mat;
     else if (m_current_matrix_mode == GL_PROJECTION)
         m_projection_matrix = m_projection_matrix * rotation_mat;
+
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_translate(GLdouble x, GLdouble y, GLdouble z)
@@ -488,6 +520,8 @@ void SoftwareGLContext::gl_translate(GLdouble x, GLdouble y, GLdouble z)
     } else if (m_current_matrix_mode == GL_PROJECTION) {
         m_projection_matrix = m_projection_matrix * FloatMatrix4x4::translate({ (float)x, (float)y, (float)z });
     }
+
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_vertex(GLdouble x, GLdouble y, GLdouble z, GLdouble w)
@@ -509,6 +543,7 @@ void SoftwareGLContext::gl_vertex(GLdouble x, GLdouble y, GLdouble z, GLdouble w
     vertex.v = 0.0f;
 
     vertex_list.append(vertex);
+    m_error = GL_NO_ERROR;
 }
 
 void SoftwareGLContext::gl_viewport(GLint x, GLint y, GLsizei width, GLsizei height)
@@ -517,6 +552,7 @@ void SoftwareGLContext::gl_viewport(GLint x, GLint y, GLsizei width, GLsizei hei
     (void)(y);
     (void)(width);
     (void)(height);
+    m_error = GL_NO_ERROR;
 }
 
 }

Userland/Libraries/LibGL/SoftwareGLContext.h

@@ -22,6 +22,7 @@ public:
     virtual void gl_color(GLdouble r, GLdouble g, GLdouble b, GLdouble a) override;
     virtual void gl_end() override;
     virtual void gl_frustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near_val, GLdouble far_val) override;
+    virtual GLenum gl_get_error() override;
     virtual GLubyte* gl_get_string(GLenum name) override;
     virtual void gl_load_identity() override;
     virtual void gl_matrix_mode(GLenum mode) override;
@@ -49,6 +50,8 @@ private:
     Vector<GLVertex> vertex_list;
     Vector<GLTriangle> triangle_list;
     Vector<GLTriangle> processed_triangles;
+
+    GLenum m_error = GL_NO_ERROR;
 };
 
 }