From 61bd1890d215dccdbdddcc9d541424299d457319 Mon Sep 17 00:00:00 2001
From: Erik Biederstadt <biederstadterik@gmail.com>
Date: Tue, 8 Jun 2021 21:34:50 -0600
Subject: [PATCH] LibGL: Implement very basic version of glGetFloatv

This is a very basic implementation of glGetfloatv. It will only give a
result when used with GL_MODELVIEW_MATRIX. In the future
 we can update and extend it's functionality.
---
 Userland/Libraries/LibGL/GL/gl.h              |  4 +++
 Userland/Libraries/LibGL/GLContext.h          |  1 +
 Userland/Libraries/LibGL/GLUtils.cpp          |  5 +++
 .../Libraries/LibGL/SoftwareGLContext.cpp     | 32 +++++++++++++++++++
 Userland/Libraries/LibGL/SoftwareGLContext.h  |  1 +
 5 files changed, 43 insertions(+)

diff --git a/Userland/Libraries/LibGL/GL/gl.h b/Userland/Libraries/LibGL/GL/gl.h
index 62af06aab0bc32..5b6325061601e3 100644
--- a/Userland/Libraries/LibGL/GL/gl.h
+++ b/Userland/Libraries/LibGL/GL/gl.h
@@ -201,6 +201,9 @@ extern "C" {
 #define GL_NEAREST_MIPMAP_LINEAR 0x2602
 #define GL_REPEAT 0x2603
 
+// OpenGL State & GLGet
+#define GL_MODELVIEW_MATRIX 0x0BA6
+
 //
 // OpenGL typedefs
 //
@@ -294,6 +297,7 @@ GLAPI void glTexImage2D(GLenum target, GLint level, GLint internalFormat, GLsize
 GLAPI void glTexCoord2f(GLfloat s, GLfloat t);
 GLAPI void glBindTexture(GLenum target, GLuint texture);
 GLAPI void glActiveTexture(GLenum texture);
+GLAPI void glGetFloatv(GLenum pname, GLfloat* params);
 
 #ifdef __cplusplus
 }
diff --git a/Userland/Libraries/LibGL/GLContext.h b/Userland/Libraries/LibGL/GLContext.h
index 7f0279f8bd288a..a352ef85961c3f 100644
--- a/Userland/Libraries/LibGL/GLContext.h
+++ b/Userland/Libraries/LibGL/GLContext.h
@@ -61,6 +61,7 @@ class GLContext {
     virtual void gl_tex_coord(GLfloat s, GLfloat t, GLfloat r, GLfloat q) = 0;
     virtual void gl_bind_texture(GLenum target, GLuint texture) = 0;
     virtual void gl_active_texture(GLenum texture) = 0;
+    virtual void gl_get_floatv(GLenum pname, GLfloat* params) = 0;
 
     virtual void present() = 0;
 };
diff --git a/Userland/Libraries/LibGL/GLUtils.cpp b/Userland/Libraries/LibGL/GLUtils.cpp
index 46ccd7f1dc6510..732315fdd041c9 100644
--- a/Userland/Libraries/LibGL/GLUtils.cpp
+++ b/Userland/Libraries/LibGL/GLUtils.cpp
@@ -84,3 +84,8 @@ void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format
 {
     g_gl_context->gl_read_pixels(x, y, width, height, format, type, pixels);
 }
+
+void glGetFloatv(GLenum pname, GLfloat* params)
+{
+    g_gl_context->gl_get_floatv(pname, params);
+}
diff --git a/Userland/Libraries/LibGL/SoftwareGLContext.cpp b/Userland/Libraries/LibGL/SoftwareGLContext.cpp
index c26e462d824a20..ec5c9dad33f266 100644
--- a/Userland/Libraries/LibGL/SoftwareGLContext.cpp
+++ b/Userland/Libraries/LibGL/SoftwareGLContext.cpp
@@ -1291,6 +1291,38 @@ void SoftwareGLContext::gl_active_texture(GLenum texture)
     m_active_texture_unit = &m_texture_units.at(texture - GL_TEXTURE0);
 }
 
+void SoftwareGLContext::gl_get_floatv(GLenum pname, GLfloat* params)
+{
+    RETURN_WITH_ERROR_IF(m_in_draw_state, GL_INVALID_OPERATION);
+
+    auto flatten_and_assign_matrix = [&params](const FloatMatrix4x4& matrix) {
+        auto elements = matrix.elements();
+
+        for (size_t i = 0; i < 4; ++i) {
+            for (size_t j = 0; j < 4; ++j) {
+                params[i * 4 + j] = elements[i][j];
+            }
+        }
+    };
+
+    switch (pname) {
+    case GL_MODELVIEW_MATRIX:
+        if (m_current_matrix_mode == GL_MODELVIEW)
+            flatten_and_assign_matrix(m_model_view_matrix);
+        else {
+            if (m_model_view_matrix_stack.is_empty())
+                flatten_and_assign_matrix(FloatMatrix4x4::identity());
+            else
+                flatten_and_assign_matrix(m_model_view_matrix_stack.last());
+        }
+        break;
+    default:
+        // FIXME: Because glQuake only requires GL_MODELVIEW_MATRIX, that is the only parameter
+        // that we currently support. More parameters should be supported.
+        TODO();
+    }
+}
+
 void SoftwareGLContext::present()
 {
     m_rasterizer.blit_to(*m_frontbuffer);
diff --git a/Userland/Libraries/LibGL/SoftwareGLContext.h b/Userland/Libraries/LibGL/SoftwareGLContext.h
index 40ab70c0ed414f..d41d92fbd77dbd 100644
--- a/Userland/Libraries/LibGL/SoftwareGLContext.h
+++ b/Userland/Libraries/LibGL/SoftwareGLContext.h
@@ -71,6 +71,7 @@ class SoftwareGLContext : public GLContext {
     virtual void gl_tex_coord(GLfloat s, GLfloat t, GLfloat r, GLfloat q) override;
     virtual void gl_bind_texture(GLenum target, GLuint texture) override;
     virtual void gl_active_texture(GLenum texture) override;
+    virtual void gl_get_floatv(GLenum pname, GLfloat* params) override;
 
     virtual void present() override;