Add nearest neighbor texture filter (#6189)

Closes https://github.com/citra-emu/citra/issues/4707
closes https://github.com/citra-emu/citra/issues/5274

src/video_core/CMakeLists.txt

@@ -69,6 +69,8 @@ add_library(video_core STATIC
     renderer_opengl/texture_filters/anime4k/anime4k_ultrafast.h
     renderer_opengl/texture_filters/bicubic/bicubic.cpp
     renderer_opengl/texture_filters/bicubic/bicubic.h
+    renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.cpp
+    renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.h
     renderer_opengl/texture_filters/scale_force/scale_force.cpp
     renderer_opengl/texture_filters/scale_force/scale_force.h
     renderer_opengl/texture_filters/texture_filter_base.h
@@ -117,6 +119,7 @@ set(SHADER_FILES
     renderer_opengl/texture_filters/anime4k/x_gradient.frag
     renderer_opengl/texture_filters/anime4k/y_gradient.frag
     renderer_opengl/texture_filters/bicubic/bicubic.frag
+    renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.frag
     renderer_opengl/texture_filters/scale_force/scale_force.frag
     renderer_opengl/texture_filters/tex_coord.vert
     renderer_opengl/texture_filters/xbrz/xbrz_freescale.frag

src/video_core/renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.cpp

@@ -0,0 +1,47 @@
+// Copyright 2022 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "video_core/renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.h"
+
+#include "shaders/nearest_neighbor.frag"
+#include "shaders/tex_coord.vert"
+
+namespace OpenGL {
+
+NearestNeighbor::NearestNeighbor(u16 scale_factor) : TextureFilterBase(scale_factor) {
+    program.Create(tex_coord_vert.data(), nearest_neighbor_frag.data());
+    vao.Create();
+    src_sampler.Create();
+
+    state.draw.shader_program = program.handle;
+    state.draw.vertex_array = vao.handle;
+    state.draw.shader_program = program.handle;
+    state.texture_units[0].sampler = src_sampler.handle;
+
+    // linear minification still makes sense
+    glSamplerParameteri(src_sampler.handle, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+    glSamplerParameteri(src_sampler.handle, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glSamplerParameteri(src_sampler.handle, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+    glSamplerParameteri(src_sampler.handle, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+}
+
+void NearestNeighbor::Filter(const OGLTexture& src_tex, Common::Rectangle<u32> src_rect,
+                             const OGLTexture& dst_tex, Common::Rectangle<u32> dst_rect) {
+    const OpenGLState cur_state = OpenGLState::GetCurState();
+    state.texture_units[0].texture_2d = src_tex.handle;
+    state.draw.draw_framebuffer = draw_fbo.handle;
+    state.viewport = {static_cast<GLint>(dst_rect.left), static_cast<GLint>(dst_rect.bottom),
+                      static_cast<GLsizei>(dst_rect.GetWidth()),
+                      static_cast<GLsizei>(dst_rect.GetHeight())};
+    state.Apply();
+
+    glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, dst_tex.handle,
+                           0);
+    glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_TEXTURE_2D, 0, 0);
+    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
+
+    cur_state.Apply();
+}
+
+} // namespace OpenGL

src/video_core/renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.frag

@@ -0,0 +1,12 @@
+//? #version 330
+precision mediump float;
+
+in vec2 tex_coord;
+
+out vec4 frag_color;
+
+uniform sampler2D input_texture;
+
+void main() {
+    frag_color = texture(input_texture, tex_coord);
+}

src/video_core/renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.h

@@ -0,0 +1,27 @@
+// Copyright 2022 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "video_core/renderer_opengl/gl_resource_manager.h"
+#include "video_core/renderer_opengl/gl_state.h"
+#include "video_core/renderer_opengl/texture_filters/texture_filter_base.h"
+
+namespace OpenGL {
+
+class NearestNeighbor : public TextureFilterBase {
+public:
+    static constexpr std::string_view NAME = "Nearest Neighbor";
+
+    explicit NearestNeighbor(u16 scale_factor);
+    void Filter(const OGLTexture& src_tex, Common::Rectangle<u32> src_rect,
+                const OGLTexture& dst_tex, Common::Rectangle<u32> dst_rect) override;
+
+private:
+    OpenGLState state{};
+    OGLProgram program{};
+    OGLVertexArray vao{};
+    OGLSampler src_sampler{};
+};
+} // namespace OpenGL

src/video_core/renderer_opengl/texture_filters/texture_filterer.cpp

@@ -8,6 +8,7 @@
 #include "common/logging/log.h"
 #include "video_core/renderer_opengl/texture_filters/anime4k/anime4k_ultrafast.h"
 #include "video_core/renderer_opengl/texture_filters/bicubic/bicubic.h"
+#include "video_core/renderer_opengl/texture_filters/nearest_neighbor/nearest_neighbor.h"
 #include "video_core/renderer_opengl/texture_filters/scale_force/scale_force.h"
 #include "video_core/renderer_opengl/texture_filters/texture_filter_base.h"
 #include "video_core/renderer_opengl/texture_filters/texture_filterer.h"
@@ -28,6 +29,7 @@ static const std::unordered_map<std::string_view, TextureFilterContructor> filte
     {TextureFilterer::NONE, [](u16) { return nullptr; }},
     FilterMapPair<Anime4kUltrafast>(),
     FilterMapPair<Bicubic>(),
+    FilterMapPair<NearestNeighbor>(),
     FilterMapPair<ScaleForce>(),
     FilterMapPair<XbrzFreescale>(),
 };

src/video_core/renderer_opengl/texture_filters/texture_filterer.h

@@ -14,7 +14,7 @@ namespace OpenGL {
 
 class TextureFilterer {
 public:
-    static constexpr std::string_view NONE = "none";
+    static constexpr std::string_view NONE = "Linear (Default)";
 
 public:
     explicit TextureFilterer(std::string_view filter_name, u16 scale_factor);