From 3d2d99817c6e27d565e084eb296320c02ee5dfee Mon Sep 17 00:00:00 2001
From: LRFLEW <lrflew@aol.com>
Date: Thu, 19 Oct 2017 18:49:26 -0500
Subject: [PATCH] OpenGL: Add Depth Buffer and Depth Test

---
 data/shaders/drawline.frag                    |  6 +--
 data/shaders/drawline.vert                    | 20 +++++---
 data/shaders/drawrect.vert                    |  7 ++-
 .../engines/opengl/CopyFramebufferShader.cpp  |  3 +-
 .../engines/opengl/CopyFramebufferShader.h    |  2 +-
 .../drawing/engines/opengl/DrawCommands.h     | 26 +++++-----
 .../drawing/engines/opengl/DrawLineShader.cpp | 50 +++++++++++--------
 .../drawing/engines/opengl/DrawLineShader.h   | 16 +++---
 .../drawing/engines/opengl/DrawRectShader.cpp |  4 ++
 .../drawing/engines/opengl/DrawRectShader.h   |  1 +
 .../drawing/engines/opengl/GLSLTypes.h        | 47 ++++++++---------
 .../engines/opengl/OpenGLDrawingEngine.cpp    | 45 +++++++++--------
 .../engines/opengl/OpenGLFramebuffer.cpp      | 10 ++++
 .../engines/opengl/OpenGLFramebuffer.h        |  1 +
 .../drawing/engines/opengl/TextureCache.h     | 16 +++---
 15 files changed, 146 insertions(+), 108 deletions(-)

diff --git a/data/shaders/drawline.frag b/data/shaders/drawline.frag
index e385164708..5348dd43a2 100644
--- a/data/shaders/drawline.frag
+++ b/data/shaders/drawline.frag
@@ -1,12 +1,10 @@
 #version 150
 
-uniform uint    uColour;
-
-in vec2 fPosition;
+flat in uint fColour;
 
 out uint oColour;
 
 void main()
 {
-    oColour = uColour;
+    oColour = fColour;
 }
diff --git a/data/shaders/drawline.vert b/data/shaders/drawline.vert
index ebbfe202ec..6e22166f9d 100644
--- a/data/shaders/drawline.vert
+++ b/data/shaders/drawline.vert
@@ -1,22 +1,30 @@
 #version 150
 
+// Allows for about 8 million draws per frame
+const float DEPTH_INCREMENT = 1.0 / float(1u << 22u);
+
 uniform ivec2 uScreenSize;
-uniform ivec4 uBounds;
-uniform ivec4 uClip;
+
+in ivec4 vBounds;
+in ivec4 vClip;
+in uint  vColour;
+in int   vDepth;
 
 in mat4x2 vVertMat;
 
-out vec2 fPosition;
+flat out uint fColour;
 
 void main()
 {
-    vec2 pos = clamp(vVertMat * uBounds, uClip.xy, uClip.zw);
-    fPosition = pos;
+    vec2 pos = clamp(vVertMat * vBounds, vClip.xy, vClip.zw);
 
     // Transform screen coordinates to viewport
     pos.x = (pos.x * (2.0 / uScreenSize.x)) - 1.0;
     pos.y = (pos.y * (2.0 / uScreenSize.y)) - 1.0;
     pos.y *= -1;
+    float depth = 1.0 - vDepth * DEPTH_INCREMENT;
 
-    gl_Position = vec4(pos, 0.0, 1.0);
+    fColour = vColour;
+
+    gl_Position = vec4(pos, depth, 1.0);
 }
diff --git a/data/shaders/drawrect.vert b/data/shaders/drawrect.vert
index 6a89106728..283fc1fe38 100644
--- a/data/shaders/drawrect.vert
+++ b/data/shaders/drawrect.vert
@@ -1,5 +1,8 @@
 #version 150
 
+// Allows for about 8 million draws per frame
+const float DEPTH_INCREMENT = 1.0 / float(1u << 22u);
+
 uniform ivec2 uScreenSize;
 
 in ivec4 vClip;
@@ -11,6 +14,7 @@ in ivec3 vPalettes;
 in int   vFlags;
 in uint  vColour;
 in ivec4 vBounds;
+in int   vDepth;
 
 in mat4x2 vVertMat;
 in vec2   vVertVec;
@@ -36,10 +40,11 @@ void main()
     pos.x = (pos.x * (2.0 / uScreenSize.x)) - 1.0;
     pos.y = (pos.y * (2.0 / uScreenSize.y)) - 1.0;
     pos.y *= -1;
+    float depth = 1.0 - vDepth * DEPTH_INCREMENT;
 
     fFlags = vFlags;
     fColour = vColour;
     fPalettes = vec3(vPalettes);
 
-    gl_Position = vec4(pos, 0.0, 1.0);
+    gl_Position = vec4(pos, depth, 1.0);
 }
diff --git a/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.cpp b/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.cpp
index db043b6d9e..34bea525ef 100644
--- a/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.cpp
+++ b/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.cpp
@@ -73,7 +73,8 @@ void CopyFramebufferShader::SetTexture(GLuint texture)
     OpenGLAPI::SetTexture(0, GL_TEXTURE_2D, texture);
 }
 
-void CopyFramebufferShader::SetPalette(const vec4f * glPalette) {
+void CopyFramebufferShader::SetPalette(const vec4 * glPalette)
+{
     glUniform4fv(uPalette, 256, (const GLfloat *)glPalette);
 }
 
diff --git a/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.h b/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.h
index 8f24fdf851..2b4dc2f8fc 100644
--- a/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.h
+++ b/src/openrct2-ui/drawing/engines/opengl/CopyFramebufferShader.h
@@ -36,7 +36,7 @@ public:
     ~CopyFramebufferShader() override;
 
     void SetTexture(GLuint texture);
-    void SetPalette(const vec4f * glPalette);
+    void SetPalette(const vec4 * glPalette);
 
     void Draw();
 
diff --git a/src/openrct2-ui/drawing/engines/opengl/DrawCommands.h b/src/openrct2-ui/drawing/engines/opengl/DrawCommands.h
index 89fda218fa..59dbe834f2 100644
--- a/src/openrct2-ui/drawing/engines/opengl/DrawCommands.h
+++ b/src/openrct2-ui/drawing/engines/opengl/DrawCommands.h
@@ -66,23 +66,25 @@ public:
 
 struct DrawLineCommand
 {
-    uint8 colour;
-    vec4i clip;
-    sint32 pos[4];
+    ivec4 clip;
+    ivec4 bounds;
+    GLuint colour;
+    GLint depth;
 };
 
 // Per-instance data for images
 struct DrawRectCommand
 {
-    vec4i clip;
-    sint32 texColourAtlas;
-    vec4f texColourBounds;
-    sint32 texMaskAtlas;
-    vec4f texMaskBounds;
-    vec3i palettes;
-    sint32 flags;
-    uint32 colour;
-    vec4i bounds;
+    ivec4 clip;
+    GLint texColourAtlas;
+    vec4 texColourBounds;
+    GLint texMaskAtlas;
+    vec4 texMaskBounds;
+    ivec3 palettes;
+    GLint flags;
+    GLuint colour;
+    ivec4 bounds;
+    GLint depth;
 
     enum
     {
diff --git a/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.cpp b/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.cpp
index 530ba25575..cbedf20613 100644
--- a/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.cpp
+++ b/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.cpp
@@ -35,6 +35,7 @@ DrawLineShader::DrawLineShader() : OpenGLShaderProgram("drawline")
     GetLocations();
 
     glGenBuffers(1, &_vbo);
+    glGenBuffers(1, &_vboInstances);
     glGenVertexArrays(1, &_vao);
 
     glBindBuffer(GL_ARRAY_BUFFER, _vbo);
@@ -46,11 +47,27 @@ DrawLineShader::DrawLineShader() : OpenGLShaderProgram("drawline")
     glVertexAttribPointer(vVertMat+2, 2, GL_FLOAT, GL_FALSE, sizeof(VDStruct), (void*) offsetof(VDStruct, mat[2]));
     glVertexAttribPointer(vVertMat+3, 2, GL_FLOAT, GL_FALSE, sizeof(VDStruct), (void*) offsetof(VDStruct, mat[3]));
 
+    glBindBuffer(GL_ARRAY_BUFFER, _vboInstances);
+    glVertexAttribIPointer(vClip, 4, GL_INT, sizeof(DrawLineCommand), (void*) offsetof(DrawLineCommand, clip));
+    glVertexAttribIPointer(vBounds, 4, GL_INT, sizeof(DrawLineCommand), (void*) offsetof(DrawLineCommand, bounds));
+    glVertexAttribIPointer(vColour, 1, GL_UNSIGNED_INT, sizeof(DrawLineCommand), (void*) offsetof(DrawLineCommand, colour));
+    glVertexAttribIPointer(vDepth, 1, GL_INT, sizeof(DrawLineCommand), (void*) offsetof(DrawLineCommand, depth));
+
     glEnableVertexAttribArray(vVertMat+0);
     glEnableVertexAttribArray(vVertMat+1);
     glEnableVertexAttribArray(vVertMat+2);
     glEnableVertexAttribArray(vVertMat+3);
 
+    glEnableVertexAttribArray(vClip);
+    glEnableVertexAttribArray(vBounds);
+    glEnableVertexAttribArray(vColour);
+    glEnableVertexAttribArray(vDepth);
+
+    glVertexAttribDivisor(vClip, 1);
+    glVertexAttribDivisor(vBounds, 1);
+    glVertexAttribDivisor(vColour, 1);
+    glVertexAttribDivisor(vDepth, 1);
+
     Use();
 }
 
@@ -63,9 +80,11 @@ DrawLineShader::~DrawLineShader()
 void DrawLineShader::GetLocations()
 {
     uScreenSize = GetUniformLocation("uScreenSize");
-    uClip       = GetUniformLocation("uClip");
-    uBounds     = GetUniformLocation("uBounds");
-    uColour     = GetUniformLocation("uColour");
+
+    vClip       = GetAttributeLocation("vClip");
+    vBounds     = GetAttributeLocation("vBounds");
+    vColour     = GetAttributeLocation("vColour");
+    vDepth      = GetAttributeLocation("vDepth");
 
     vVertMat    = GetAttributeLocation("vVertMat");
 }
@@ -75,27 +94,14 @@ void DrawLineShader::SetScreenSize(sint32 width, sint32 height)
     glUniform2i(uScreenSize, width, height);
 }
 
-void DrawLineShader::SetClip(sint32 left, sint32 top, sint32 right, sint32 bottom)
+void DrawLineShader::DrawInstances(const LineCommandBatch& instances)
 {
-    glUniform4i(uClip, left, top, right, bottom);
-}
-
-void DrawLineShader::SetBounds(sint32 x0, sint32 y0, sint32 x1, sint32 y1)
-{
-    glUniform4i(uBounds, x0, y0, x1, y1);
-}
-
-void DrawLineShader::SetColour(uint8 colour)
-{
-    glUniform1ui(uColour, colour);
-}
-
-void DrawLineShader::Draw(sint32 x0, sint32 y0, sint32 x1, sint32 y1)
-{
-    SetBounds(x0, y0, x1, y1);
-
     glBindVertexArray(_vao);
-    glDrawArrays(GL_LINES, 0, 2);
+
+    glBindBuffer(GL_ARRAY_BUFFER, _vboInstances);
+    glBufferData(GL_ARRAY_BUFFER, sizeof(DrawLineCommand) * instances.size(), instances.data(), GL_STREAM_DRAW);
+
+    glDrawArraysInstanced(GL_LINES, 0, 2, (GLsizei)instances.size());
 }
 
 #endif /* DISABLE_OPENGL */
diff --git a/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.h b/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.h
index 176da2edd7..f6ef652eec 100644
--- a/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.h
+++ b/src/openrct2-ui/drawing/engines/opengl/DrawLineShader.h
@@ -18,18 +18,22 @@
 
 #include "GLSLTypes.h"
 #include "OpenGLShaderProgram.h"
+#include "DrawCommands.h"
 
 class DrawLineShader final : public OpenGLShaderProgram
 {
 private:
     GLuint uScreenSize;
-    GLuint uClip;
-    GLuint uBounds;
-    GLuint uColour;
+
+    GLuint vClip;
+    GLuint vBounds;
+    GLuint vColour;
+    GLuint vDepth;
 
     GLuint vVertMat;
 
     GLuint _vbo;
+    GLuint _vboInstances;
     GLuint _vao;
 
 public:
@@ -37,11 +41,7 @@ public:
     ~DrawLineShader() override;
 
     void SetScreenSize(sint32 width, sint32 height);
-    void SetClip(sint32 left, sint32 top, sint32 right, sint32 bottom);
-    void SetBounds(sint32 x0, sint32 y0, sint32 x1, sint32 y1);
-    void SetColour(uint8 colour);
-
-    void Draw(sint32 x0, sint32 y0, sint32 x1, sint32 y1);
+    void DrawInstances(const LineCommandBatch& instances);
 
 private:
     void GetLocations();
diff --git a/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.cpp b/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.cpp
index 31985ca626..80d60819c6 100644
--- a/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.cpp
+++ b/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.cpp
@@ -61,6 +61,7 @@ DrawRectShader::DrawRectShader() : OpenGLShaderProgram("drawrect")
     glVertexAttribIPointer(vFlags, 1, GL_INT, sizeof(DrawRectCommand), (void*) offsetof(DrawRectCommand, flags));
     glVertexAttribIPointer(vColour, 1, GL_UNSIGNED_INT, sizeof(DrawRectCommand), (void*) offsetof(DrawRectCommand, colour));
     glVertexAttribIPointer(vBounds, 4, GL_INT, sizeof(DrawRectCommand), (void*) offsetof(DrawRectCommand, bounds));
+    glVertexAttribIPointer(vDepth, 1, GL_INT, sizeof(DrawRectCommand), (void*) offsetof(DrawRectCommand, depth));
 
     glEnableVertexAttribArray(vVertMat+0);
     glEnableVertexAttribArray(vVertMat+1);
@@ -77,6 +78,7 @@ DrawRectShader::DrawRectShader() : OpenGLShaderProgram("drawrect")
     glEnableVertexAttribArray(vFlags);
     glEnableVertexAttribArray(vColour);
     glEnableVertexAttribArray(vBounds);
+    glEnableVertexAttribArray(vDepth);
 
     glVertexAttribDivisor(vClip, 1);
     glVertexAttribDivisor(vTexColourAtlas, 1);
@@ -87,6 +89,7 @@ DrawRectShader::DrawRectShader() : OpenGLShaderProgram("drawrect")
     glVertexAttribDivisor(vFlags, 1);
     glVertexAttribDivisor(vColour, 1);
     glVertexAttribDivisor(vBounds, 1);
+    glVertexAttribDivisor(vDepth, 1);
 
     Use();
     glUniform1i(uTexture, 0);
@@ -115,6 +118,7 @@ void DrawRectShader::GetLocations()
     vFlags              = GetAttributeLocation("vFlags");
     vColour             = GetAttributeLocation("vColour");
     vBounds             = GetAttributeLocation("vBounds");
+    vDepth              = GetAttributeLocation("vDepth");
 
     vVertMat            = GetAttributeLocation("vVertMat");
     vVertVec            = GetAttributeLocation("vVertVec");
diff --git a/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h b/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h
index 4081d20c02..756852a18e 100644
--- a/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h
+++ b/src/openrct2-ui/drawing/engines/opengl/DrawRectShader.h
@@ -41,6 +41,7 @@ private:
     GLuint vFlags;
     GLuint vColour;
     GLuint vBounds;
+    GLuint vDepth;
 
     GLuint _vbo;
     GLuint _vboInstances;
diff --git a/src/openrct2-ui/drawing/engines/opengl/GLSLTypes.h b/src/openrct2-ui/drawing/engines/opengl/GLSLTypes.h
index 074f2193fd..4fa4285f52 100644
--- a/src/openrct2-ui/drawing/engines/opengl/GLSLTypes.h
+++ b/src/openrct2-ui/drawing/engines/opengl/GLSLTypes.h
@@ -17,49 +17,50 @@
 #pragma once
 
 #include <openrct2/common.h>
+#include "OpenGLAPI.h"
 
 #pragma pack(push, 1)
 
-struct vec2i
+struct ivec2
 {
-    union { sint32 x; sint32 s; sint32 r; };
-    union { sint32 y; sint32 t; sint32 g; };
+    union { GLint x; GLint s; GLint r; };
+    union { GLint y; GLint t; GLint g; };
 };
 
-struct vec2f
+struct vec2
 {
-    union { float x; float s; float r; };
-    union { float y; float t; float g; };
+    union { GLfloat x; GLfloat s; GLfloat r; };
+    union { GLfloat y; GLfloat t; GLfloat g; };
 };
 
-struct vec3i
+struct ivec3
 {
-    union { sint32 x; sint32 s; sint32 r; };
-    union { sint32 y; sint32 t; sint32 g; };
-    union { sint32 z; sint32 p; sint32 b; };
+    union { GLint x; GLint s; GLint r; };
+    union { GLint y; GLint t; GLint g; };
+    union { GLint z; GLint p; GLint b; };
 };
 
 struct vec3f
 {
-    union { float x; float s; float r; };
-    union { float y; float t; float g; };
-    union { float z; float p; float b; };
+    union { GLfloat x; GLfloat s; GLfloat r; };
+    union { GLfloat y; GLfloat t; GLfloat g; };
+    union { GLfloat z; GLfloat p; GLfloat b; };
 };
 
-struct vec4i
+struct ivec4
 {
-    union { sint32 x; sint32 s; sint32 r; };
-    union { sint32 y; sint32 t; sint32 g; };
-    union { sint32 z; sint32 p; sint32 b; };
-    union { sint32 w; sint32 q; sint32 a; };
+    union { GLint x; GLint s; GLint r; };
+    union { GLint y; GLint t; GLint g; };
+    union { GLint z; GLint p; GLint b; };
+    union { GLint w; GLint q; GLint a; };
 };
 
-struct vec4f
+struct vec4
 {
-    union { float x; float s; float r; };
-    union { float y; float t; float g; };
-    union { float z; float p; float b; };
-    union { float w; float q; float a; };
+    union { GLfloat x; GLfloat s; GLfloat r; };
+    union { GLfloat y; GLfloat t; GLfloat g; };
+    union { GLfloat z; GLfloat p; GLfloat b; };
+    union { GLfloat w; GLfloat q; GLfloat a; };
 };
 
 #pragma pack(pop)
diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp b/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp
index e23c84bd74..6f2e6243f3 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLDrawingEngine.cpp
@@ -79,7 +79,10 @@ private:
     sint32 _clipRight  = 0;
     sint32 _clipBottom = 0;
 
-    struct {
+    sint32 _drawCount  = 0;
+
+    struct
+    {
         LineCommandBatch lines;
         RectCommandBatch rects;
     } _commandBuffers;
@@ -94,6 +97,7 @@ public:
     void Initialise();
     void Resize(sint32 width, sint32 height);
     void ResetPalette();
+    void ResetDrawCount() { _drawCount = 0; }
 
     void Clear(uint8 paletteIndex) override;
     void FillRect(uint32 colour, sint32 x, sint32 y, sint32 w, sint32 h) override;
@@ -135,7 +139,7 @@ private:
 
 public:
     SDL_Color Palette[256];
-    vec4f     GLPalette[256];
+    vec4      GLPalette[256];
 
     OpenGLDrawingEngine(IUiContext * uiContext)
         : _uiContext(uiContext)
@@ -228,7 +232,9 @@ public:
         assert(_screenFramebuffer != nullptr);
         assert(_swapFramebuffer != nullptr);
 
+        _drawingContext->ResetDrawCount();
         _swapFramebuffer->Bind();
+        glClear(GL_DEPTH_BUFFER_BIT);
     }
 
     void EndDraw() override
@@ -236,6 +242,7 @@ public:
         _drawingContext->FlushCommandBuffers();
 
         // Scale up to window
+        glDisable(GL_DEPTH_TEST);
         _screenFramebuffer->Bind();
         _copyFramebufferShader->Use();
         _copyFramebufferShader->SetTexture(_swapFramebuffer->GetTargetFramebuffer()->GetTexture());
@@ -453,8 +460,9 @@ void OpenGLDrawingContext::FillRect(uint32 colour, sint32 left, sint32 top, sint
     command.texMaskBounds = { 0.0f, 0.0f, 0.0f, 0.0f };
     command.palettes = { 0, 0, 0 };
     command.colour = colour & 0xFF;
-    command.bounds = { left + _offsetX, top + _offsetY, right + 1, bottom + 1 };
+    command.bounds = { left, top, right + 1, bottom + 1 };
     command.flags = DrawRectCommand::FLAG_NO_TEXTURE;
+    command.depth = _drawCount++;
 
     if (colour & 0x1000000)
     {
@@ -519,17 +527,10 @@ void OpenGLDrawingContext::DrawLine(uint32 colour, sint32 x1, sint32 y1, sint32
 
     DrawLineCommand& command = _commandBuffers.lines.allocate();
 
-    command.colour = colour & 0xFF;
-
     command.clip = { _clipLeft, _clipTop, _clipRight, _clipBottom };
-
-    command.pos[0] = x1;
-    command.pos[1] = y1;
-    command.pos[2] = x2;
-    command.pos[3] = y2;
-
-    // Must be rendered in order right now, because it does not yet use depth
-    FlushCommandBuffers();
+    command.bounds = { x1, y1, x2, y2 };
+    command.colour = colour & 0xFF;
+    command.depth = _drawCount++;
 }
 
 void OpenGLDrawingContext::DrawSprite(uint32 image, sint32 x, sint32 y, uint32 tertiaryColour)
@@ -610,7 +611,7 @@ void OpenGLDrawingContext::DrawSprite(uint32 image, sint32 x, sint32 y, uint32 t
     auto texture = _textureCache->GetOrLoadImageTexture(image);
 
     int paletteCount;
-    vec3i palettes{};
+    ivec3 palettes{};
     bool special = false;
     if (image & IMAGE_TYPE_REMAP_2_PLUS)
     {
@@ -657,6 +658,7 @@ void OpenGLDrawingContext::DrawSprite(uint32 image, sint32 x, sint32 y, uint32 t
     command.colour = 0;
     command.bounds = { left, top, right, bottom };
     command.flags = paletteCount;
+    command.depth = _drawCount++;
 }
 
 void OpenGLDrawingContext::DrawSpriteRawMasked(sint32 x, sint32 y, uint32 maskImage, uint32 colourImage)
@@ -714,6 +716,7 @@ void OpenGLDrawingContext::DrawSpriteRawMasked(sint32 x, sint32 y, uint32 maskIm
     command.flags = DrawRectCommand::FLAG_MASK;
     command.colour = 0;
     command.bounds = { left, top, right, bottom };
+    command.depth = _drawCount++;
 }
 
 void OpenGLDrawingContext::DrawSpriteSolid(uint32 image, sint32 x, sint32 y, uint8 colour)
@@ -760,6 +763,7 @@ void OpenGLDrawingContext::DrawSpriteSolid(uint32 image, sint32 x, sint32 y, uin
     command.flags = DrawRectCommand::FLAG_NO_TEXTURE | DrawRectCommand::FLAG_MASK;
     command.colour = colour & 0xFF;
     command.bounds = { left, top, right, bottom };
+    command.depth = _drawCount++;
 }
 
 void OpenGLDrawingContext::DrawGlyph(uint32 image, sint32 x, sint32 y, uint8 * palette)
@@ -804,25 +808,22 @@ void OpenGLDrawingContext::DrawGlyph(uint32 image, sint32 x, sint32 y, uint8 * p
     command.flags = 0;
     command.colour = 0;
     command.bounds = { left, top, right, bottom };
+    command.depth = _drawCount++;
 }
 
 void OpenGLDrawingContext::FlushCommandBuffers()
 {
+    glEnable(GL_DEPTH_TEST);
     FlushLines();
     FlushRectangles();
 }
 
 void OpenGLDrawingContext::FlushLines() 
 {
-    for (size_t n = 0; n < _commandBuffers.lines.size(); n++)
-    {
-        const auto& command = _commandBuffers.lines[n];
+    if (_commandBuffers.lines.size() == 0) return;
 
-        _drawLineShader->Use();
-        _drawLineShader->SetColour(command.colour);
-        _drawLineShader->SetClip(command.clip.x, command.clip.y, command.clip.z, command.clip.w);
-        _drawLineShader->Draw(command.pos[0], command.pos[1], command.pos[2], command.pos[3]);
-    }
+    _drawLineShader->Use();
+    _drawLineShader->DrawInstances(_commandBuffers.lines);
 
     _commandBuffers.lines.reset();
 }
diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp
index 4f2f20a172..f29696809a 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.cpp
@@ -27,6 +27,7 @@ OpenGLFramebuffer::OpenGLFramebuffer(SDL_Window * window)
 {
     _id = BACKBUFFER_ID;
     _texture = 0;
+    _depth = 0;
     SDL_GetWindowSize(window, &_width, &_height);
 }
 
@@ -41,9 +42,17 @@ OpenGLFramebuffer::OpenGLFramebuffer(sint32 width, sint32 height)
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
     glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 
+    glGenTextures(1, &_depth);
+    glBindTexture(GL_TEXTURE_2D, _depth);
+    glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT24, width, height, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, nullptr);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
+    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_NONE);
+
     glGenFramebuffers(1, &_id);
     glBindFramebuffer(GL_FRAMEBUFFER, _id);
     glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, _texture, 0);
+    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, _depth, 0);
 }
 
 OpenGLFramebuffer::~OpenGLFramebuffer()
@@ -51,6 +60,7 @@ OpenGLFramebuffer::~OpenGLFramebuffer()
     if (_id != BACKBUFFER_ID)
     {
         glDeleteTextures(1, &_texture);
+        glDeleteTextures(1, &_depth);
         glDeleteFramebuffers(1, &_id);
     }
 }
diff --git a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h
index 9b1d3e2747..374b0b4926 100644
--- a/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h
+++ b/src/openrct2-ui/drawing/engines/opengl/OpenGLFramebuffer.h
@@ -29,6 +29,7 @@ class OpenGLFramebuffer
 private:
     GLuint _id;
     GLuint _texture;
+    GLuint _depth;
     sint32 _width;
     sint32 _height;
 
diff --git a/src/openrct2-ui/drawing/engines/opengl/TextureCache.h b/src/openrct2-ui/drawing/engines/opengl/TextureCache.h
index 21879fc27c..7171438727 100644
--- a/src/openrct2-ui/drawing/engines/opengl/TextureCache.h
+++ b/src/openrct2-ui/drawing/engines/opengl/TextureCache.h
@@ -65,9 +65,9 @@ struct CachedTextureInfo
 {
     GLuint index;
     GLuint slot;
-    vec4i bounds;
-    vec4f normalizedBounds;
-    vec4f computedBounds;
+    ivec4 bounds;
+    vec4 normalizedBounds;
+    vec4 computedBounds;
 };
 
 // Represents a texture atlas that images of a given maximum size can be allocated from
@@ -159,12 +159,12 @@ public:
     }
 
 private:
-    vec4i GetSlotCoordinates(GLuint slot, sint32 actualWidth, sint32 actualHeight) const
+    ivec4 GetSlotCoordinates(GLuint slot, sint32 actualWidth, sint32 actualHeight) const
     {
         sint32 row = slot / _cols;
         sint32 col = slot % _cols;
 
-        return vec4i
+        return ivec4
         {
             _imageSize * col,
             _imageSize * row,
@@ -173,14 +173,14 @@ private:
         };
     }
 
-    vec4f NormalizeCoordinates(const vec4i& coords) const
+    vec4 NormalizeCoordinates(const ivec4& coords) const
     {
-        return vec4f
+        return vec4
         {
             coords.x / (float) _atlasWidth,
             coords.y / (float) _atlasHeight,
             coords.z / (float) _atlasWidth,
-            coords.w / (float) _atlasHeight
+            coords.w / (float) _atlasHeight,
         };
     }
 };