From bfeb3d2d51e419bc4429915e24bce181ffec134a Mon Sep 17 00:00:00 2001
From: bjorn <tie.372@gmail.com>
Date: Fri, 26 Oct 2018 09:14:57 -0700
Subject: [PATCH] lovr.graphics.discard;

---
 src/api/graphics.c      | 10 ++++++++++
 src/graphics/graphics.c |  6 ++++++
 src/graphics/graphics.h |  2 ++
 src/graphics/opengl.c   | 26 ++++++++++++++++++++++++++
 4 files changed, 44 insertions(+)

diff --git a/src/api/graphics.c b/src/api/graphics.c
index 18dda691..24c6c991 100644
--- a/src/api/graphics.c
+++ b/src/api/graphics.c
@@ -635,6 +635,15 @@ static int l_lovrGraphicsClear(lua_State* L) {
   return 0;
 }
 
+static int l_lovrGraphicsDiscard(lua_State* L) {
+  int top = lua_gettop(L);
+  bool color = top >= 1 ? lua_toboolean(L, 1) : true;
+  bool depth = top >= 2 ? lua_toboolean(L, 2) : true;
+  bool stencil = top >= 3 ? lua_toboolean(L, 3) : true;
+  lovrGraphicsDiscard(color, depth, stencil);
+  return 0;
+}
+
 static int l_lovrGraphicsPoints(lua_State* L) {
   uint32_t count = luax_readvertices(L, 1);
   lovrGraphicsPoints(count);
@@ -1313,6 +1322,7 @@ static const luaL_Reg lovrGraphics[] = {
 
   // Rendering
   { "clear", l_lovrGraphicsClear },
+  { "discard", l_lovrGraphicsDiscard },
   { "points", l_lovrGraphicsPoints },
   { "line", l_lovrGraphicsLine },
   { "triangle", l_lovrGraphicsTriangle },
diff --git a/src/graphics/graphics.c b/src/graphics/graphics.c
index 9a8a9081..b4db4a98 100644
--- a/src/graphics/graphics.c
+++ b/src/graphics/graphics.c
@@ -398,6 +398,12 @@ void lovrGraphicsClear(Color* color, float* depth, int* stencil) {
   lovrGpuClear(canvas, color, depth, stencil);
 }
 
+void lovrGraphicsDiscard(bool color, bool depth, bool stencil) {
+  Pipeline* pipeline = &state.pipelines[state.pipeline];
+  Canvas* canvas = pipeline->canvas ? pipeline->canvas : state.camera.canvas;
+  lovrGpuDiscard(canvas, color, depth, stencil);
+}
+
 void lovrGraphicsDraw(DrawCommand* draw) {
   Mesh* mesh = draw->mesh;
   if (!mesh) {
diff --git a/src/graphics/graphics.h b/src/graphics/graphics.h
index b3149a0a..6d5d7d5a 100644
--- a/src/graphics/graphics.h
+++ b/src/graphics/graphics.h
@@ -211,6 +211,7 @@ void lovrGraphicsSetProjection(mat4 projection);
 // Rendering
 VertexPointer lovrGraphicsGetVertexPointer(uint32_t capacity);
 void lovrGraphicsClear(Color* color, float* depth, int* stencil);
+void lovrGraphicsDiscard(bool color, bool depth, bool stencil);
 void lovrGraphicsDraw(DrawCommand* draw);
 void lovrGraphicsPoints(uint32_t count);
 void lovrGraphicsLine(uint32_t count);
@@ -237,6 +238,7 @@ void lovrGpuDestroy();
 void lovrGpuBindPipeline(Pipeline* pipeline);
 void lovrGpuSetViewports(float* viewports, int count);
 void lovrGpuClear(Canvas* canvas, Color* color, float* depth, int* stencil);
+void lovrGpuDiscard(Canvas* canvas, bool color, bool depth, bool stencil);
 void lovrGpuStencil(StencilAction action, int replaceValue, StencilCallback callback, void* userdata);
 void lovrGpuCompute(Shader* shader, int x, int y, int z);
 void lovrGpuPresent();
diff --git a/src/graphics/opengl.c b/src/graphics/opengl.c
index 17e15892..690000f5 100644
--- a/src/graphics/opengl.c
+++ b/src/graphics/opengl.c
@@ -859,6 +859,32 @@ void lovrGpuClear(Canvas* canvas, Color* color, float* depth, int* stencil) {
   }
 }
 
+void lovrGpuDiscard(Canvas* canvas, bool color, bool depth, bool stencil) {
+#if defined(EMSCRIPTEN) || defined(__ANDROID__)
+  lovrCanvasBind(canvas, false);
+
+  GLenum attachments[MAX_CANVAS_ATTACHMENTS + 1] = { 0 };
+  int count = 0;
+
+  if (color) {
+    int n = canvas ? canvas->attachmentCount : 1;
+    for (int i = 0; i < n; i++) {
+      attachments[count++] = GL_COLOR_ATTACHMENT0 + i;
+    }
+  }
+
+  if (depth) {
+    attachments[count++] = GL_DEPTH_ATTACHMENT;
+  }
+
+  if (stencil) {
+    attachments[count++] = GL_STENCIL_ATTACHMENT;
+  }
+
+  glInvalidateFramebuffer(GL_FRAMEBUFFER, count, attachments);
+#endif
+}
+
 void lovrGpuStencil(StencilAction action, int replaceValue, StencilCallback callback, void* userdata) {
   state.depthWrite = false;
   glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);