Rendering loop rewrite (#339)

* PlatformCore: Remove erroneus OpenGL call

* PlatformCore: Add GBA screen size constants

* PlatformCore: Switch to drawing a triangle strip

Vertices' origin at the bottom left, CCW order.

* PlatformCore: Cleanup types

* PlatformCore: Extract setting texture parameters

Also set texture wrapping parameters to eliminate artifacts on the edges
of the output image when using linear sampling.

* PlatformCore: Extract setting shader uniforms

* PlatformCore: Add output size shader uniform

And use it in xBRZ shader.

* PlatformCore: Rename u_screen_map into u_input_map

* PlatformCore: Add flipped UV generic vertex shader

* PlatformCore: Adjust setting viewport

* PlatformCore: Upload texture data via glTexSubImage

* PlatformCore: Rewrite rendering loop

Introduce ShaderPass object, which holds shader program and input/output
texture indices.

src/platform/core/include/platform/device/ogl_video_device.hpp

@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <array>
 #include <nba/device/video_device.hpp>
 #include <GL/glew.h>
 #include <platform/config.hpp>
@@ -27,7 +28,9 @@ struct OGLVideoDevice : VideoDevice {
   void ReloadConfig();
 
 private:
+  void UpdateTextures();
   void CreateShaderPrograms();
+  void UpdateShaderUniforms();
   void ReleaseShaderPrograms();
 
   auto CompileShader(
@@ -40,6 +43,19 @@ struct OGLVideoDevice : VideoDevice {
     char const* fragment_src
   ) -> std::pair<bool, GLuint>;
 
+  static constexpr size_t input_index       = 0;
+  static constexpr size_t output_index      = 1;
+  static constexpr size_t history_index     = 2;
+  static constexpr size_t xbrz_output_index = 3;
+
+  struct ShaderPass {
+    GLuint program = 0;
+    struct {
+      std::vector<GLuint> inputs = {input_index};
+      GLuint output = output_index;
+    } textures = {};
+  };
+
   int view_x = 0;
   int view_y = 0;
   int view_width  = 1;
@@ -49,10 +65,9 @@ struct OGLVideoDevice : VideoDevice {
   GLuint quad_vao;
   GLuint quad_vbo;
   GLuint fbo;
-  GLuint texture[4];
-  std::vector<GLuint> programs;
-  GLenum texture_filter = GL_NEAREST;
-  bool texture_filter_invalid = false;
+  std::array<GLuint, 4> textures        = {};
+  std::vector<ShaderPass> shader_passes = {};
+  GLint texture_filter = GL_NEAREST;
 
   std::shared_ptr<PlatformConfig> config;
 };