render: A bunch of high-level improvements.

- high-level filters out duplicate render commands from the queue so
  backends don't have to.
- Setting draw color is now a render command, so backends can put color
  information into the vertex buffer to upload with everything else instead
  of setting it with slower dynamic data later.
- backends can request that they always batch, even for legacy programs,
  since the lowlevel API can deal with it (Metal, and eventually Vulkan
  and such...)
- high-level makes sure the queue has at least one setdrawcolor and
  setviewport command before any draw calls, so the backends don't ever have
  to manage cases where this hasn't been explicitly set yet.
- backends allocating vertex buffer space can specify alignment, and the
  high-level will keep track of gaps in the buffer between the last used
  positions and the aligned data that can be used for later allocations
  (Metal and such need to specify some constant data on 256 byte boundaries,
  but we don't want to waste all that space we had to skip to meet alignment
  requirements).

src/render/SDL_render.c

@@ -109,7 +109,10 @@ static char texture_magic;
 static int
 FlushRenderCommands(SDL_Renderer *renderer)
 {
+    SDL_AllocVertGap *prevgap = &renderer->vertex_data_gaps;
+    SDL_AllocVertGap *gap = prevgap;
     int retval;
+
     SDL_assert((renderer->render_commands == NULL) == (renderer->render_commands_tail == NULL));
 
     if (renderer->render_commands == NULL) {  /* nothing to do! */
@@ -119,6 +122,14 @@ FlushRenderCommands(SDL_Renderer *renderer)
 
     retval = renderer->RunCommandQueue(renderer, renderer->render_commands, renderer->vertex_data, renderer->vertex_data_used);
 
+    while (gap) {
+        prevgap = gap;
+        gap = gap->next;
+    }
+    prevgap->next = renderer->vertex_data_gaps_pool;
+    renderer->vertex_data_gaps_pool = renderer->vertex_data_gaps.next;
+    renderer->vertex_data_gaps.next = NULL;
+
     /* Move the whole render command queue to the unused pool so we can reuse them next time. */
     if (renderer->render_commands_tail != NULL) {
         renderer->render_commands_tail->next = renderer->render_commands_pool;
@@ -128,6 +139,9 @@ FlushRenderCommands(SDL_Renderer *renderer)
     }
     renderer->vertex_data_used = 0;
     renderer->render_command_generation++;
+    renderer->color_queued = SDL_FALSE;
+    renderer->viewport_queued = SDL_FALSE;
+    renderer->cliprect_queued = SDL_FALSE;
     return retval;
 }
 
@@ -148,14 +162,77 @@ FlushRenderCommandsIfNotBatching(SDL_Renderer *renderer)
     return renderer->batching ? 0 : FlushRenderCommands(renderer);
 }
 
-void *
-SDL_AllocateRenderVertices(SDL_Renderer *renderer, const size_t numbytes, size_t *offset)
+static SDL_AllocVertGap *
+AllocateVertexGap(SDL_Renderer *renderer)
 {
-    const size_t needed = renderer->vertex_data_used + numbytes;
+    SDL_AllocVertGap *retval = renderer->vertex_data_gaps_pool;
+    if (retval) {
+        renderer->vertex_data_gaps_pool = retval->next;
+        retval->next = NULL;
+    } else {
+        retval = (SDL_AllocVertGap *) SDL_malloc(sizeof (SDL_AllocVertGap));
+        if (!retval) {
+            SDL_OutOfMemory();
+        }
+    }
+    return retval;
+}
+
+
+void *
+SDL_AllocateRenderVertices(SDL_Renderer *renderer, const size_t numbytes, const size_t alignment, size_t *offset)
+{
+    const size_t needed = renderer->vertex_data_used + numbytes + alignment;
+    size_t aligner, aligned;
     void *retval;
 
+    SDL_AllocVertGap *prevgap = &renderer->vertex_data_gaps;
+    SDL_AllocVertGap *gap = prevgap->next;
+    while (gap) {
+        const size_t gapoffset = gap->offset;
+        aligner = (alignment && ((gap->offset % alignment) != 0)) ? (alignment - (gap->offset % alignment)) : 0;
+        aligned = gapoffset + aligner;
+
+        /* Can we use this gap? */
+        if ((aligner < gap->len) && ((gap->len - aligner) >= numbytes)) {
+            /* we either finished this gap off, trimmed the left, trimmed the right, or split it into two gaps. */
+            if (gap->len == numbytes) {  /* finished it off, remove it */
+                SDL_assert(aligned == gapoffset);
+                prevgap->next = gap->next;
+                gap->next = renderer->vertex_data_gaps_pool;
+                renderer->vertex_data_gaps_pool = gap;
+            } else if (aligned == gapoffset) {  /* trimmed the left */
+                gap->offset += numbytes;
+                gap->len -= numbytes;
+            } else if (((aligned - gapoffset) + numbytes) == gap->len) {  /* trimmed the right */
+                gap->len -= numbytes;
+            } else {  /* split into two gaps */
+                SDL_AllocVertGap *newgap = AllocateVertexGap(renderer);
+                if (!newgap) {
+                    return NULL;
+                }
+                newgap->offset = aligned + numbytes;
+                newgap->len = gap->len - (aligner + numbytes);
+                newgap->next = gap->next;
+                // gap->offset doesn't change.
+                gap->len = aligner;
+                gap->next = newgap;
+            }
+
+            if (offset) {
+                *offset = aligned;
+            }
+            return ((Uint8 *) renderer->vertex_data) + aligned;
+        }
+
+        /* Try the next gap */
+        prevgap = gap;
+        gap = gap->next;
+    }
+
+    /* no gaps with enough space; get a new piece of the vertex buffer */
     while (needed > renderer->vertex_data_allocation) {
-        const size_t current_allocation = renderer->vertex_data ? renderer->vertex_data_allocation : 128;
+        const size_t current_allocation = renderer->vertex_data ? renderer->vertex_data_allocation : 1024;
         const size_t newsize = current_allocation * 2;
         void *ptr = SDL_realloc(renderer->vertex_data, newsize);
         if (ptr == NULL) {
@@ -166,12 +243,26 @@ SDL_AllocateRenderVertices(SDL_Renderer *renderer, const size_t numbytes, size_t
         renderer->vertex_data_allocation = newsize;
     }
 
-    retval = ((Uint8 *) renderer->vertex_data) + renderer->vertex_data_used;
+    aligner = (alignment && ((renderer->vertex_data_used % alignment) != 0)) ? (alignment - (renderer->vertex_data_used % alignment)) : 0;
+    aligned = renderer->vertex_data_used + aligner;
+
+    retval = ((Uint8 *) renderer->vertex_data) + aligned;
     if (offset) {
-        *offset = renderer->vertex_data_used;
+        *offset = aligned;
     }
 
-    renderer->vertex_data_used += numbytes;
+    if (aligner) {  /* made a new gap... */
+        SDL_AllocVertGap *newgap = AllocateVertexGap(renderer);
+        if (newgap) {  /* just let it slide as lost space if malloc fails. */
+            newgap->offset = renderer->vertex_data_used;
+            newgap->len = aligner;
+            newgap->next = NULL;
+            prevgap->next = newgap;
+        }
+    }
+
+    renderer->vertex_data_used += aligner + numbytes;
+
     return retval;
 }
 
@@ -205,30 +296,77 @@ AllocateRenderCommand(SDL_Renderer *renderer)
 }
 
 static int
-QueueCmdUpdateViewport(SDL_Renderer *renderer)
+QueueCmdSetViewport(SDL_Renderer *renderer)
 {
+    int retval = 0;
+    if (!renderer->viewport_queued || (SDL_memcmp(&renderer->viewport, &renderer->last_queued_viewport, sizeof (SDL_Rect)) != 0)) {
         SDL_RenderCommand *cmd = AllocateRenderCommand(renderer);
-    if (cmd == NULL) {
-        return -1;
-    }
-
+        retval = -1;
+        if (cmd != NULL) {
             cmd->command = SDL_RENDERCMD_SETVIEWPORT;
-    SDL_memcpy(&cmd->data.viewport, &renderer->viewport, sizeof (cmd->data.viewport));
-    return FlushRenderCommandsIfNotBatching(renderer);
+            cmd->data.viewport.first = 0;  /* render backend will fill this in. */
+            SDL_memcpy(&cmd->data.viewport.rect, &renderer->viewport, sizeof (renderer->viewport));
+            retval = renderer->QueueSetViewport(renderer, cmd);
+            if (retval < 0) {
+                cmd->command = SDL_RENDERCMD_NO_OP;
+            } else {
+                SDL_memcpy(&renderer->last_queued_viewport, &renderer->viewport, sizeof (SDL_Rect));
+                renderer->viewport_queued = SDL_TRUE;
+            }
+        }
+    }
+    return retval < 0 ? retval : FlushRenderCommandsIfNotBatching(renderer);
 }
 
 static int
-QueueCmdUpdateClipRect(SDL_Renderer *renderer)
+QueueCmdSetClipRect(SDL_Renderer *renderer)
 {
+    int retval = 0;
+    if ((!renderer->cliprect_queued) ||
+         (renderer->clipping_enabled != renderer->last_queued_cliprect_enabled) ||
+         (SDL_memcmp(&renderer->clip_rect, &renderer->last_queued_cliprect, sizeof (SDL_Rect)) != 0)) {
         SDL_RenderCommand *cmd = AllocateRenderCommand(renderer);
         if (cmd == NULL) {
-        return -1;
-    }
-
+            retval = -1;
+        } else {
             cmd->command = SDL_RENDERCMD_SETCLIPRECT;
             cmd->data.cliprect.enabled = renderer->clipping_enabled;
             SDL_memcpy(&cmd->data.cliprect.rect, &renderer->clip_rect, sizeof (cmd->data.cliprect.rect));
-    return FlushRenderCommandsIfNotBatching(renderer);
+            SDL_memcpy(&renderer->last_queued_cliprect, &renderer->clip_rect, sizeof (SDL_Rect));
+            renderer->last_queued_cliprect_enabled = renderer->clipping_enabled;
+            renderer->cliprect_queued = SDL_TRUE;
+        }
+    }
+    return retval < 0 ? retval : FlushRenderCommandsIfNotBatching(renderer);
+}
+
+static int
+QueueCmdSetDrawColor(SDL_Renderer *renderer, const Uint8 r, const Uint8 g, const Uint8 b, const Uint8 a)
+{
+    const Uint32 color = ((a << 24) | (r << 16) | (g << 8) | b);
+    int retval = 0;
+    
+    if (!renderer->color_queued || (color != renderer->last_queued_color)) {
+        SDL_RenderCommand *cmd = AllocateRenderCommand(renderer);
+        retval = -1;
+
+        if (cmd != NULL) {
+            cmd->command = SDL_RENDERCMD_SETDRAWCOLOR;
+            cmd->data.color.first = 0;  /* render backend will fill this in. */
+            cmd->data.color.r = r;
+            cmd->data.color.g = g;
+            cmd->data.color.b = b;
+            cmd->data.color.a = a;
+            retval = renderer->QueueSetDrawColor(renderer, cmd);
+            if (retval < 0) {
+                cmd->command = SDL_RENDERCMD_NO_OP;
+            } else {
+                renderer->last_queued_color = color;
+                renderer->color_queued = SDL_TRUE;
+            }
+        }
+    }
+    return retval < 0 ? retval : FlushRenderCommandsIfNotBatching(renderer);
 }
 
 static int
@@ -240,6 +378,7 @@ QueueCmdClear(SDL_Renderer *renderer)
     }
 
     cmd->command = SDL_RENDERCMD_CLEAR;
+    cmd->data.color.first = 0;
     cmd->data.color.r = renderer->r;
     cmd->data.color.g = renderer->g;
     cmd->data.color.b = renderer->b;
@@ -247,10 +386,28 @@ QueueCmdClear(SDL_Renderer *renderer)
     return FlushRenderCommandsIfNotBatching(renderer);
 }
 
+static int
+PrepQueueCmdDraw(SDL_Renderer *renderer, const Uint8 r, const Uint8 g, const Uint8 b, const Uint8 a)
+{
+    int retval = 0;
+    if (retval == 0) {
+        retval = QueueCmdSetDrawColor(renderer, r, g, b, a);
+    }
+    if (retval == 0) {
+        retval = QueueCmdSetViewport(renderer);
+    }
+    if (retval == 0) {
+        retval = QueueCmdSetClipRect(renderer);
+    }
+    return retval;
+}
+
 static SDL_RenderCommand *
 PrepQueueCmdDrawSolid(SDL_Renderer *renderer, const SDL_RenderCommandType cmdtype)
 {
-    SDL_RenderCommand *cmd = AllocateRenderCommand(renderer);
+    SDL_RenderCommand *cmd = NULL;
+    if (PrepQueueCmdDraw(renderer, renderer->r, renderer->g, renderer->b, renderer->a) == 0) {
+        cmd = AllocateRenderCommand(renderer);
         if (cmd != NULL) {
             cmd->command = cmdtype;
             cmd->data.draw.first = 0;  /* render backend will fill this in. */
@@ -262,6 +419,7 @@ PrepQueueCmdDrawSolid(SDL_Renderer *renderer, const SDL_RenderCommandType cmdtyp
             cmd->data.draw.blend = renderer->blendMode;
             cmd->data.draw.texture = NULL;  /* no texture. */
         }
+    }
     return cmd;
 }
 
@@ -310,7 +468,9 @@ QueueCmdFillRects(SDL_Renderer *renderer, const SDL_FRect * rects, const int cou
 static SDL_RenderCommand *
 PrepQueueCmdDrawTexture(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_RenderCommandType cmdtype)
 {
-    SDL_RenderCommand *cmd = AllocateRenderCommand(renderer);
+    SDL_RenderCommand *cmd = NULL;
+    if (PrepQueueCmdDraw(renderer, texture->r, texture->g, texture->b, texture->a) == 0) {
+        cmd = AllocateRenderCommand(renderer);
         if (cmd != NULL) {
             cmd->command = cmdtype;
             cmd->data.draw.first = 0;  /* render backend will fill this in. */
@@ -322,6 +482,7 @@ PrepQueueCmdDrawTexture(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_
             cmd->data.draw.blend = texture->blendMode;
             cmd->data.draw.texture = texture;
         }
+    }
     return cmd;
 }
 
@@ -435,7 +596,7 @@ SDL_RendererEventWatch(void *userdata, SDL_Event *event)
                         renderer->viewport.y = 0;
                         renderer->viewport.w = w;
                         renderer->viewport.h = h;
-                        QueueCmdUpdateViewport(renderer);
+                        QueueCmdSetViewport(renderer);
                     }
                 }
 
@@ -557,6 +718,8 @@ void VerifyDrawQueueFunctions(const SDL_Renderer *renderer)
 {
     /* all of these functions are required to be implemented, even as no-ops, so we don't
         have to check that they aren't NULL over and over. */
+    SDL_assert(renderer->QueueSetViewport != NULL);
+    SDL_assert(renderer->QueueSetDrawColor != NULL);
     SDL_assert(renderer->QueueDrawPoints != NULL);
     SDL_assert(renderer->QueueDrawLines != NULL);
     SDL_assert(renderer->QueueFillRects != NULL);
@@ -641,7 +804,9 @@ SDL_CreateRenderer(SDL_Window * window, int index, Uint32 flags)
         VerifyDrawQueueFunctions(renderer);
 
         /* let app/user override batching decisions. */
-        if (SDL_GetHint(SDL_HINT_RENDER_BATCHING)) {
+        if (renderer->always_batch) {
+            batching = SDL_TRUE;
+        } else if (SDL_GetHint(SDL_HINT_RENDER_BATCHING)) {
             batching = SDL_GetHintBoolean(SDL_HINT_RENDER_BATCHING, SDL_TRUE);
         }
 
@@ -1557,10 +1722,10 @@ SDL_SetRenderTarget(SDL_Renderer *renderer, SDL_Texture *texture)
 
     SDL_UnlockMutex(renderer->target_mutex);
 
-    if (QueueCmdUpdateViewport(renderer) < 0) {
+    if (QueueCmdSetViewport(renderer) < 0) {
         return -1;
     }
-    if (QueueCmdUpdateClipRect(renderer) < 0) {
+    if (QueueCmdSetClipRect(renderer) < 0) {
         return -1;
     }
 
@@ -1751,7 +1916,7 @@ SDL_RenderSetViewport(SDL_Renderer * renderer, const SDL_Rect * rect)
             return -1;
         }
     }
-    return QueueCmdUpdateViewport(renderer);
+    return QueueCmdSetViewport(renderer);
 }
 
 void
@@ -1782,7 +1947,7 @@ SDL_RenderSetClipRect(SDL_Renderer * renderer, const SDL_Rect * rect)
         renderer->clipping_enabled = SDL_FALSE;
         SDL_zero(renderer->clip_rect);
     }
-    return QueueCmdUpdateClipRect(renderer);
+    return QueueCmdSetClipRect(renderer);
 }
 
 void
@@ -2412,6 +2577,8 @@ void
 SDL_DestroyRenderer(SDL_Renderer * renderer)
 {
     SDL_RenderCommand *cmd;
+    SDL_AllocVertGap *gap;
+    SDL_AllocVertGap *nextgap;
 
     CHECK_RENDERER_MAGIC(renderer, );
 
@@ -2436,6 +2603,16 @@ SDL_DestroyRenderer(SDL_Renderer * renderer)
 
     SDL_free(renderer->vertex_data);
 
+    for (gap = renderer->vertex_data_gaps.next; gap; gap = nextgap) {
+        nextgap = gap->next;
+        SDL_free(gap);
+    }
+
+    for (gap = renderer->vertex_data_gaps_pool; gap; gap = nextgap) {
+        nextgap = gap->next;
+        SDL_free(gap);
+    }
+
     /* Free existing textures for this renderer */
     while (renderer->textures) {
         SDL_Texture *tex = renderer->textures; (void) tex;

src/render/SDL_sysrender.h

@@ -88,6 +88,7 @@ typedef enum
     SDL_RENDERCMD_NO_OP,
     SDL_RENDERCMD_SETVIEWPORT,
     SDL_RENDERCMD_SETCLIPRECT,
+    SDL_RENDERCMD_SETDRAWCOLOR,
     SDL_RENDERCMD_CLEAR,
     SDL_RENDERCMD_DRAW_POINTS,
     SDL_RENDERCMD_DRAW_LINES,
@@ -100,7 +101,10 @@ typedef struct SDL_RenderCommand
 {
     SDL_RenderCommandType command;
     union {
-        SDL_Rect viewport;
+        struct {
+            size_t first;
+            SDL_Rect rect;
+        } viewport;
         struct {
             SDL_bool enabled;
             SDL_Rect rect;
@@ -113,12 +117,20 @@ typedef struct SDL_RenderCommand
             SDL_Texture *texture;
         } draw;
         struct {
+            size_t first;
             Uint8 r, g, b, a;
         } color;
     } data;
     struct SDL_RenderCommand *next;
 } SDL_RenderCommand;
 
+typedef struct SDL_AllocVertGap
+{
+    size_t offset;
+    size_t len;
+    struct SDL_AllocVertGap *next;
+} SDL_AllocVertGap;
+
 
 /* Define the SDL renderer structure */
 struct SDL_Renderer
@@ -129,6 +141,8 @@ struct SDL_Renderer
     int (*GetOutputSize) (SDL_Renderer * renderer, int *w, int *h);
     SDL_bool (*SupportsBlendMode)(SDL_Renderer * renderer, SDL_BlendMode blendMode);
     int (*CreateTexture) (SDL_Renderer * renderer, SDL_Texture * texture);
+    int (*QueueSetViewport) (SDL_Renderer * renderer, SDL_RenderCommand *cmd);
+    int (*QueueSetDrawColor) (SDL_Renderer * renderer, SDL_RenderCommand *cmd);
     int (*QueueDrawPoints) (SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_FPoint * points,
                              int count);
     int (*QueueDrawLines) (SDL_Renderer * renderer, SDL_RenderCommand *cmd, const SDL_FPoint * points,
@@ -209,15 +223,25 @@ struct SDL_Renderer
     Uint8 r, g, b, a;                   /**< Color for drawing operations values */
     SDL_BlendMode blendMode;            /**< The drawing blend mode */
 
+    SDL_bool always_batch;
     SDL_bool batching;
     SDL_RenderCommand *render_commands;
     SDL_RenderCommand *render_commands_tail;
     SDL_RenderCommand *render_commands_pool;
     Uint32 render_command_generation;
+    Uint32 last_queued_color;
+    SDL_Rect last_queued_viewport;
+    SDL_Rect last_queued_cliprect;
+    SDL_bool last_queued_cliprect_enabled;
+    SDL_bool color_queued;
+    SDL_bool viewport_queued;
+    SDL_bool cliprect_queued;
 
     void *vertex_data;
     size_t vertex_data_used;
     size_t vertex_data_allocation;
+    SDL_AllocVertGap vertex_data_gaps;
+    SDL_AllocVertGap *vertex_data_gaps_pool;
 
     void *driverdata;
 };
@@ -253,7 +277,7 @@ extern SDL_BlendOperation SDL_GetBlendModeAlphaOperation(SDL_BlendMode blendMode
 /* drivers call this during their Queue*() methods to make space in a array that are used
    for a vertex buffer during RunCommandQueue(). Pointers returned here are only valid until
    the next call, because it might be in an array that gets realloc()'d. */
-extern void *SDL_AllocateRenderVertices(SDL_Renderer *renderer, const size_t numbytes, size_t *offset);
+extern void *SDL_AllocateRenderVertices(SDL_Renderer *renderer, const size_t numbytes, const size_t alignment, size_t *offset);
 
 #endif /* SDL_sysrender_h_ */