sokol_imgui.h: rewrite rendering code to only do one buffer update pe…

…r frame (fixes #399)
floooh · Feb 14, 2021 · 5034be8 · 5034be8
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -2,7 +2,11 @@
 
 > NOTE: this list will usually only be updated with changes that affect the public APIs
 
-- **13-Fev-2021**: A new utility header [sokol_nuklear.h](https://github.com/floooh/sokol/blob/master/util/sokol_nuklear.h)
+- **14-Feb-2021**: The Dear ImGui rendering backend in [sokol_imgui.h](https://github.com/floooh/sokol/blob/master/util/sokol_imgui.h) has been rewritten to only do a single
+buffer-update per frame each for vertex- and index-data. This addresses performance-problems
+with sg_append_buffer() in the GL backend on some platforms (see [this issue](https://github.com/floooh/sokol/issues/399) for details.
+
+- **13-Feb-2021**: A new utility header [sokol_nuklear.h](https://github.com/floooh/sokol/blob/master/util/sokol_nuklear.h)
 has been added which implements a rendering backend for [Nuklear](https://github.com/Immediate-Mode-UI/Nuklear)
 on top of sokol_gfx.h. Also see the new sample [nuklear-sapp](https://floooh.github.io/sokol-html5/nuklear-sapp.html).
 Many thanks to **@wmerrifield** for the PR!

diff --git a/README.md b/README.md
@@ -6,7 +6,7 @@ Simple
 [STB-style](https://github.com/nothings/stb/blob/master/docs/stb_howto.txt)
 cross-platform libraries for C and C++, written in C.
 
-[**See what's new**](https://github.com/floooh/sokol/blob/master/CHANGELOG.md) (**12-Feb-2021**: new utility header **sokol_nuklear.h**)
+[**See what's new**](https://github.com/floooh/sokol/blob/master/CHANGELOG.md) (**14-Feb-2021**: more efficient vertex- and index-data updating in sokol_imgui.h)
 
 ## Examples and Related Projects
 

diff --git a/util/sokol_imgui.h b/util/sokol_imgui.h
@@ -42,6 +42,8 @@
     to override defaults:
 
     SOKOL_ASSERT(c)     - your own assert macro (default: assert(c))
+    SOKOL_MALLOC(s)     - your own malloc function (default: malloc(s))
+    SOKOL_FREE(p)       - your own free function (default: free(p))
     SOKOL_IMGUI_API_DECL- public function declaration prefix (default: extern)
     SOKOL_API_DECL      - same as SOKOL_IMGUI_API_DECL
     SOKOL_API_IMPL      - public function implementation prefix (default: -)
@@ -286,6 +288,11 @@ inline void simgui_setup(const simgui_desc_t& desc) { return simgui_setup(&desc)
     #include <assert.h>
     #define SOKOL_ASSERT(c) assert(c)
 #endif
+#ifndef SOKOL_MALLOC
+    #include <stdlib.h>
+    #define SOKOL_MALLOC(s) malloc(s)
+    #define SOKOL_FREE(p) free(p)
+#endif
 #ifndef _SOKOL_PRIVATE
     #if defined(__GNUC__) || defined(__clang__)
         #define _SOKOL_PRIVATE __attribute__((unused)) static
@@ -312,6 +319,10 @@ typedef struct {
     sg_shader shd;
     sg_pipeline pip;
     bool is_osx;    // return true if running on OSX (or HTML5 OSX), needed for copy/paste
+
+    sg_range vertices;
+    sg_range indices;
+
     #if !defined(SOKOL_IMGUI_NO_SOKOL_APP)
     bool btn_down[SAPP_MAX_MOUSEBUTTONS];
     bool btn_up[SAPP_MAX_MOUSEBUTTONS];
@@ -1617,6 +1628,15 @@ SOKOL_API_IMPL void simgui_setup(const simgui_desc_t* desc) {
        since sokol_gfx.h will do its own default-value handling
     */
 
+    /* allocate an intermediate vertex- and index-buffer */
+    SOKOL_ASSERT(_simgui.desc.max_vertices > 0);
+    _simgui.vertices.size = (size_t)_simgui.desc.max_vertices * sizeof(ImDrawVert);
+    _simgui.vertices.ptr = SOKOL_MALLOC(_simgui.vertices.size);
+    SOKOL_ASSERT(_simgui.vertices.ptr);
+    _simgui.indices.size = (size_t)_simgui.desc.max_vertices * 3 * sizeof(ImDrawIdx);
+    _simgui.indices.ptr = SOKOL_MALLOC(_simgui.indices.size);
+    SOKOL_ASSERT(_simgui.indices.ptr);
+
     /* initialize Dear ImGui */
     #if defined(__cplusplus)
         ImGui::CreateContext();
@@ -1672,15 +1692,15 @@ SOKOL_API_IMPL void simgui_setup(const simgui_desc_t* desc) {
     sg_buffer_desc vb_desc;
     memset(&vb_desc, 0, sizeof(vb_desc));
     vb_desc.usage = SG_USAGE_STREAM;
-    vb_desc.size = (size_t)_simgui.desc.max_vertices * sizeof(ImDrawVert);
+    vb_desc.size = _simgui.vertices.size;
     vb_desc.label = "sokol-imgui-vertices";
     _simgui.vbuf = sg_make_buffer(&vb_desc);
 
     sg_buffer_desc ib_desc;
     memset(&ib_desc, 0, sizeof(ib_desc));
     ib_desc.type = SG_BUFFERTYPE_INDEXBUFFER;
     ib_desc.usage = SG_USAGE_STREAM;
-    ib_desc.size = (size_t)_simgui.desc.max_vertices * 3 * sizeof(uint16_t);
+    ib_desc.size = _simgui.indices.size;
     ib_desc.label = "sokol-imgui-indices";
     _simgui.ibuf = sg_make_buffer(&ib_desc);
 
@@ -1814,6 +1834,10 @@ SOKOL_API_IMPL void simgui_shutdown(void) {
     sg_destroy_buffer(_simgui.ibuf);
     sg_destroy_buffer(_simgui.vbuf);
     sg_pop_debug_group();
+    SOKOL_ASSERT(_simgui.vertices.ptr);
+    SOKOL_FREE((void*)_simgui.vertices.ptr);
+    SOKOL_ASSERT(_simgui.indices.ptr);
+    SOKOL_FREE((void*)_simgui.indices.ptr);
 }
 
 #if !defined(SOKOL_IMGUI_NO_SOKOL_APP)
@@ -1887,10 +1911,60 @@ SOKOL_API_IMPL void simgui_render(void) {
     if (draw_data->CmdListsCount == 0) {
         return;
     }
+    /* copy vertices and indices into an intermediate buffer so that
+       they can be updated with a single sg_update_buffer() call each
+       (sg_append_buffer() has performance problems on some GL platforms)
+    */
+    size_t all_vtx_size = 0;
+    size_t all_idx_size = 0;
+    int cl_index = 0;
+    for (; cl_index < draw_data->CmdListsCount; cl_index++) {
+        ImDrawList* cl = draw_data->CmdLists[cl_index];
+        #if defined(__cplusplus)
+            const size_t vtx_size = cl->VtxBuffer.size() * sizeof(ImDrawVert);
+            const size_t idx_size = cl->IdxBuffer.size() * sizeof(ImDrawIdx);
+            const ImDrawVert* vtx_ptr = &cl->VtxBuffer.front();
+            const ImDrawIdx* idx_ptr = &cl->IdxBuffer.front();
+        #else
+            const size_t vtx_size = (size_t)cl->VtxBuffer.Size * sizeof(ImDrawVert);
+            const size_t idx_size = (size_t)cl->IdxBuffer.Size * sizeof(ImDrawIdx);
+            const ImDrawVert* vtx_ptr = cl->VtxBuffer.Data;
+            const ImDrawIdx* idx_ptr = cl->IdxBuffer.Data;
+        #endif
 
-    /* render the ImGui command list */
+        /* check for buffer overflow */
+        if (((all_vtx_size + vtx_size) > _simgui.vertices.size) ||
+            ((all_idx_size + idx_size) > _simgui.indices.size))
+        {
+            break;
+        }
+
+        /* copy vertices and indices into common buffers */
+        void* dst_vtx_ptr = (void*) (((uint8_t*)_simgui.vertices.ptr) + all_vtx_size);
+        void* dst_idx_ptr = (void*) (((uint8_t*)_simgui.indices.ptr) + all_idx_size);
+        memcpy(dst_vtx_ptr, vtx_ptr, vtx_size);
+        memcpy(dst_idx_ptr, idx_ptr, idx_size);
+        all_vtx_size += vtx_size;
+        all_idx_size += idx_size;
+    }
+    /* ...in case there was a buffer overflow, restrict the number of
+       command list items that are actually rendered
+    */
+    const int cmd_list_count = cl_index;
+    if (0 == cmd_list_count) {
+        return;
+    }
+
+    /* update the sokol-gfx vertex- and index-buffer */
     sg_push_debug_group("sokol-imgui");
+    sg_range vtx_data = _simgui.vertices;
+    vtx_data.size = all_vtx_size;
+    sg_range idx_data = _simgui.indices;
+    idx_data.size = all_idx_size;
+    sg_update_buffer(_simgui.vbuf, &vtx_data);
+    sg_update_buffer(_simgui.ibuf, &idx_data);
 
+    /* render the ImGui command list */
     const float dpi_scale = _simgui.desc.dpi_scale;
     const int fb_width = (int) (io->DisplaySize.x * dpi_scale);
     const int fb_height = (int) (io->DisplaySize.y * dpi_scale);
@@ -1911,38 +1985,9 @@ SOKOL_API_IMPL void simgui_render(void) {
     bind.fs_images[0].id = (uint32_t)(uintptr_t)tex_id;
     int vb_offset = 0;
     int ib_offset = 0;
-    for (int cl_index = 0; cl_index < draw_data->CmdListsCount; cl_index++) {
-        ImDrawList* cl = draw_data->CmdLists[cl_index];
+    for (int cl_index = 0; cl_index < cmd_list_count; cl_index++) {
+        const ImDrawList* cl = draw_data->CmdLists[cl_index];
 
-        /* append vertices and indices to buffers, record start offsets in draw state */
-        #if defined(__cplusplus)
-            const size_t vtx_size = cl->VtxBuffer.size() * sizeof(ImDrawVert);
-            const size_t idx_size = cl->IdxBuffer.size() * sizeof(ImDrawIdx);
-            const ImDrawVert* vtx_ptr = &cl->VtxBuffer.front();
-            const ImDrawIdx* idx_ptr = &cl->IdxBuffer.front();
-        #else
-            const size_t vtx_size = (size_t)cl->VtxBuffer.Size * sizeof(ImDrawVert);
-            const size_t idx_size = (size_t)cl->IdxBuffer.Size * sizeof(ImDrawIdx);
-            const ImDrawVert* vtx_ptr = cl->VtxBuffer.Data;
-            const ImDrawIdx* idx_ptr = cl->IdxBuffer.Data;
-        #endif
-        if (vtx_ptr) {
-            const sg_range vtx_range = { vtx_ptr, vtx_size };
-            vb_offset = sg_append_buffer(bind.vertex_buffers[0], &vtx_range);
-        }
-        if (idx_ptr) {
-            const sg_range idx_range = { idx_ptr, idx_size };
-            ib_offset = sg_append_buffer(bind.index_buffer, &idx_range);
-        }
-        /* don't render anything if the buffer is in overflow state (this is also
-            checked internally in sokol_gfx, draw calls that attempt to draw with
-            overflowed buffers will be silently dropped)
-        */
-        if (sg_query_buffer_overflow(bind.vertex_buffers[0]) ||
-            sg_query_buffer_overflow(bind.index_buffer))
-        {
-            break;
-        }
         bind.vertex_buffer_offsets[0] = vb_offset;
         bind.index_buffer_offset = ib_offset;
         sg_apply_bindings(&bind);
@@ -1981,6 +2026,15 @@ SOKOL_API_IMPL void simgui_render(void) {
             }
             base_element += (int)pcmd->ElemCount;
         }
+        #if defined(__cplusplus)
+            const size_t vtx_size = cl->VtxBuffer.size() * sizeof(ImDrawVert);
+            const size_t idx_size = cl->IdxBuffer.size() * sizeof(ImDrawIdx);
+        #else
+            const size_t vtx_size = (size_t)cl->VtxBuffer.Size * sizeof(ImDrawVert);
+            const size_t idx_size = (size_t)cl->IdxBuffer.Size * sizeof(ImDrawIdx);
+        #endif
+        vb_offset += vtx_size;
+        ib_offset += idx_size;
     }
     sg_apply_viewport(0, 0, fb_width, fb_height, true);
     sg_apply_scissor_rect(0, 0, fb_width, fb_height, true);