Add basic coarse X scrolling

src/nes.c

@@ -71,7 +71,7 @@ void nes_reset(nes* sys) {
     nes_apu_reset(&sys->apu);
 }
 
-int nes_run(nes* sys, int master_cycles, int* run) {
+nes_ppu_Result nes_run(nes* sys, int master_cycles, int* run) {
     int cpu_run = 0;
     int cpu_cycles = (master_cycles + (nes_clock_cpu_div - 1)) /
                      nes_clock_cpu_div;
@@ -79,11 +79,19 @@ int nes_run(nes* sys, int master_cycles, int* run) {
 
     master_cycles = cpu_run * nes_clock_cpu_div;
     int ppu_cycles = master_cycles / nes_clock_ppu_div;
-    int vblank = nes_ppu_run(&sys->ppu, ppu_cycles);
+    nes_ppu_Result result = nes_ppu_run(&sys->ppu, ppu_cycles);
 
-    e6502_set_nmi(&sys->cpu, vblank);
+    if (result == ppu_Result_VBlank_On) {
+        e6502_set_nmi(&sys->cpu, 1);
+    } else if (result == ppu_Result_VBlank_Off) {
+        e6502_set_nmi(&sys->cpu, 0);
+    }
 
     if (run) *run = master_cycles;
 
-    return status;
+    if (status < 0) {
+        result = ppu_Result_Halt;
+    }
+
+    return result;
 }

src/nes.h

@@ -59,7 +59,7 @@ void nes_init(nes*);
 
 void nes_reset(nes*);
 
-int nes_run(nes*, int cycles, int* run);
+nes_ppu_Result nes_run(nes*, int cycles, int* run);
 
 
 #endif // NES_H_

src/nese.c

@@ -72,15 +72,17 @@ int main(int argc, char* argv[]) {
         nes_init(&sys);
         nes_reset(&sys);
 
+        nes_render(rend, &sys.ppu);
+
         struct timespec t_target = {0};
         clock_gettime(CLOCK_MONOTONIC, &t_target);
         uint64_t cycle_last_frame = 0;
 
         uint64_t total_cycles = 0;
-        int last_frame_rendered = -1;
+//        int last_frame_rendered = -1;
         for (int i = 0; i < n_loops && status == 0; ++i) {
             int run = 0;
-            status = nes_run(&sys, nes_clock_cpu_div, &run);
+            nes_ppu_Result result = nes_run(&sys, 1U, &run);
             total_cycles += run;
 /*
             float us_run = (    run * 1000. * 1000. *
@@ -90,26 +92,32 @@ int main(int argc, char* argv[]) {
                             us_run, run,
                             status == 0 ? "OK" : "Halted");
 */
-            if (    status == 0 &&
-                    sys.ppu.frame != last_frame_rendered) {
-                // TODO: Check VBlank or scanline?
+            if (    result == ppu_Result_Ready ||
+                    result == ppu_Result_VBlank_Off) {
                 status = nes_render(rend, &sys.ppu);
-                last_frame_rendered = sys.ppu.frame;
 
-                // Sleep to catch up to master clock
-                uint64_t elapsed_cycles = total_cycles -
-                                          cycle_last_frame;
-                int elapsed_ns = (  elapsed_cycles *
-                                    nes_clock_master_den *
-                                    NS_PER_S ) /
-                                 nes_clock_master_num;
+                if (status > 0) {
+//                    last_frame_rendered = sys.ppu.frame;
+
+                    // Sleep to catch up to master clock
+                    uint64_t elapsed_cycles = total_cycles -
+                                              cycle_last_frame;
+                    int elapsed_ns = (  elapsed_cycles *
+                                        nes_clock_master_den *
+                                        NS_PER_S ) /
+                                     nes_clock_master_num;
+
+                    t_add_ns(&t_target, &t_target, elapsed_ns);
 
-                t_add_ns(&t_target, &t_target, elapsed_ns);
+                    clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME,
+                                    &t_target, NULL);
 
-                clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME,
-                                &t_target, NULL);
+                    cycle_last_frame = total_cycles;
 
-                cycle_last_frame = total_cycles;
+                    status = 0;
+                }
+            } else if (result == ppu_Result_Halt) {
+                status = -1;
             }
         }
 

src/ppu.c

@@ -147,7 +147,7 @@ void nes_ppu_init(nes_ppu* ppu, uint8_t* chr_mem) {
 }
 
 int nes_ppu_run(nes_ppu* ppu, int cycles) {
-    int vblank = 0;
+    nes_ppu_Result result = ppu_Result_Running;
 
     ppu->cycle += cycles;
 
@@ -167,15 +167,18 @@ int nes_ppu_run(nes_ppu* ppu, int cycles) {
             ppu->status &= ~(ppu_Status_VBlank | ppu_Status_Hit);
             ppu->hit_line = 0;
             ppu->hit_dot = 0;
-            ppu->scanline -= nes_ppu_frame;
+            ppu->scanline = 0;
             ppu->frame++;
-            // TODO: Render callback if vblank was previously set?
+            result = ppu_Result_VBlank_Off;
 
         } else if (ppu->scanline >= nes_ppu_active) {
             ppu->status |= ppu_Status_VBlank;
             if (ppu->control & ppu_Control_VBlank) {
-                vblank = 1;
+                result = ppu_Result_VBlank_On;
             }
+
+        } else if (ppu->scanline % 8 == 1) {
+            result = ppu_Result_Ready;
         }
     }
 
@@ -185,13 +188,14 @@ int nes_ppu_run(nes_ppu* ppu, int cycles) {
         ppu->status |= ppu_Status_Hit;
     }
 
-    return vblank;
+    return result;
 }
 
-
+/*
 int nes_ppu_cycles_til_vblank(nes_ppu* ppu) {
     int cycles_til_vblank = nes_ppu_active_cycles - (
             ppu->cycle + (ppu->scanline * nes_ppu_dots));
     return (cycles_til_vblank > 0 ? cycles_til_vblank :
             nes_ppu_vblank_cycles + cycles_til_vblank);
 }
+*/

src/ppu.h

@@ -47,6 +47,8 @@
 
 typedef enum {
     ppu_Control_Nametable_Mask  = 0b00000011,
+    ppu_Control_Scroll_Page_X   = 0b00000001,
+    ppu_Control_Scroll_Page_Y   = 0b00000010,
     ppu_Control_VRAM_Inc        = 0b00000100,
     ppu_Control_Sprite_Bank     = 0b00001000,
     ppu_Control_Back_Bank       = 0b00010000,
@@ -108,7 +110,15 @@ void nes_ppu_write(nes_ppu* ppu, uint16_t addr, uint8_t val);
 void nes_ppu_reset(nes_ppu* ppu);
 void nes_ppu_init(nes_ppu* ppu, uint8_t* chr_mem);
 
-int nes_ppu_run(nes_ppu* ppu, int cycles);
-int nes_ppu_cycles_til_vblank(nes_ppu* ppu);
+typedef enum {
+    ppu_Result_Halt     = -1,
+    ppu_Result_Running  = 0U,
+    ppu_Result_VBlank_On,
+    ppu_Result_VBlank_Off,
+    ppu_Result_Ready,
+} nes_ppu_Result;
+
+nes_ppu_Result nes_ppu_run(nes_ppu* ppu, int cycles);
+//int nes_ppu_cycles_til_vblank(nes_ppu* ppu);
 
 #endif // ENES_PPU_H_

src/sdl_render.c

@@ -84,7 +84,7 @@ static int sdl_render_init(nes_Renderer* rend) {
 
     if (0 == status) {
         data->background = SDL_CreateRGBSurfaceWithFormat(
-                0, nes_ppu_render_w, nes_ppu_render_h,
+                0, nes_ppu_render_w + 8, nes_ppu_render_h + 8,
                 8, SDL_PIXELFORMAT_INDEX8
             );
 
@@ -159,13 +159,13 @@ typedef enum {
     Render_Mode_Sprite      = 0b00000,
     Render_Mode_Background  = 0b00001,
     Render_Mode_Behind      = 0b00010,
-    Render_Mode_Collide     = 0b00100,
+//    Render_Mode_Collide     = 0b00100,
     Render_Mode_Flip_X      = 0b01000,
     Render_Mode_Flip_Y      = 0b10000,
 } Render_Mode;
 
 
-static void render_bg_sprite(nes_ppu* ppu, int index,
+static void render_bg_sprite(const nes_ppu* ppu, int index,
                              const uint8_t* pal,
                              void* loc, int pitch) {
     uint8_t* sprite = &ppu->chr_mem[index * 16U];
@@ -187,31 +187,80 @@ static void render_bg_sprite(nes_ppu* ppu, int index,
     }
 }
 
-// TODO: Don't re-render background unless VRAM/scroll changes
-
-static void render_background(nes_ppu* ppu, int nametable,
-                              void* buffer, int pitch) {
+static void render_background_area(const nes_ppu* ppu, int page,
+                                   void* buffer, int pitch,
+                                   int xs, int ys, int w, int h) {
     int bank = (ppu->control & ppu_Control_Back_Bank) ? 0x100 : 0;
-    // TODO: Support beyond nametable 0
-    const uint8_t* index = &ppu->vram[nametable * 0x400U];
-    const uint8_t* attrs = index + 960U;
+    const uint8_t* index_line = &ppu->vram[page * 0x400U];
+    const uint8_t* attrs = index_line + 960U;
+    index_line += xs + (ys * nes_ppu_blocks_w);
     uint8_t* dst_line = (uint8_t*)buffer;
-    for (int y = 0; y < nes_ppu_blocks_h; ++y) {
+    for (int y = ys; y < h + ys; ++y) {
         uint8_t* dst = dst_line;
-        for (int x = 0; x < nes_ppu_blocks_w; ++x) {
-            if (x > 0 || (ppu->mask & ppu_Mask_Left_Back)) {
-                int attr_idx = ((y / 4) * 8) + (x / 4);
-                int shift = 2 * ((y & 0b10) | ((x & 0b10) >> 1));
-                int pal_idx = (attrs[attr_idx] >> shift) & 3;
-                const uint8_t* pal = &ppu->palette[pal_idx * 4];
-                render_bg_sprite(ppu, bank + *index, pal,
-                                 dst, pitch);
-            }
+        const uint8_t* index = index_line;
+        for (int x = xs; x < w + xs; ++x) {
+            int attr_idx = ((y / 4) * 8) + (x / 4);
+            int shift = 2 * ((y & 0b10) | ((x & 0b10) >> 1));
+            int pal_idx = (attrs[attr_idx] >> shift) & 3;
+            const uint8_t* pal = &ppu->palette[pal_idx * 4];
+            render_bg_sprite(ppu, bank + *index, pal,
+                             dst, pitch);
             ++index;
             dst += 8;
         }
         dst_line += pitch * 8;
+        index_line += nes_ppu_blocks_w;
+    }
+}
+
+static void render_background_line(const nes_ppu* ppu, int line,
+                                   void* buffer, int pitch) {
+    int scroll_x = ppu->scroll_x;
+    if (ppu->control & ppu_Control_Scroll_Page_X) {
+        // TODO: This looks like a kludge.  Why check for 0?
+        if (scroll_x != 0) scroll_x += nes_ppu_render_w;
+    }
+
+/*
+    int scroll_y = ppu->scroll_y + (
+                   (ppu->control & ppu_Control_Scroll_Page_Y) ?
+                   nes_ppu_render_h : 0);
+*/
+    int block_x = scroll_x / 8;
+/*
+    int block_y = scroll_y / 8;
+    int fine_x = scroll_x % 8;
+    int fine_y = scroll_y % 8;
+*/
+
+    // TODO: Handle vertical scrolling
+    // TODO: Handle column 0 flag
+
+    buffer += line * pitch * 8U;
+
+    // Left
+
+    int page = 0;
+    int x = block_x;
+    if (x >= nes_ppu_blocks_w) {
+        x -= nes_ppu_blocks_w;
+        page += 1;
     }
+
+    render_background_area(
+            ppu, page, buffer, pitch,
+            x, line,
+            nes_ppu_blocks_w - x, 1
+        );
+
+    // Right
+
+    buffer += (nes_ppu_blocks_w - x) * 8U;
+    render_background_area(
+            ppu, 1U - page, buffer, pitch,
+            0, line,
+            1U + x, 1
+        );
 }
 
 static int render_sprite(nes_ppu* ppu, int index,
@@ -244,6 +293,7 @@ static int render_sprite(nes_ppu* ppu, int index,
             int pal_idx = ( ((hi & 0x80) >> 6) |
                             ((lo & 0x80) >> 7));
             int nes_pal_idx = (pal_idx ? pal[pal_idx] : 0xFFU);
+/*
             if (    hit_pos < 0 &&
                     (ppu->mask & ppu_Mask_Back) &&
                     (mode & Render_Mode_Collide) &&
@@ -251,6 +301,7 @@ static int render_sprite(nes_ppu* ppu, int index,
                     *back != 0xFFU ) {
                 hit_pos = (8 - x) + (8 * (8 - y));
             }
+*/
             if ((mode & Render_Mode_Behind) && *back != 0xFFU) {
                 nes_pal_idx = 0xFFU;
             }
@@ -286,6 +337,51 @@ typedef enum {
     oam_Index_Tile_Mask = 0b11111110,
 } oam_Index;
 
+// Check sprite (0 only) collision on a scanline
+// This assumes that we've verified that this sprite
+// intersects with this scanline.
+static int eval_sprite_line(const nes_ppu* ppu, int line,
+                            const oam_sprite* sprite,
+                            const uint8_t* chr,
+                            const uint8_t* back) {
+    int hit_pos = -1;
+
+    int y = line - (sprite->y + 1);
+
+    if (sprite->attr & oam_Attr_Flip_Y) y = 7 - y;
+    uint8_t lo = chr[0U + y];
+    uint8_t hi = chr[8U + y];
+
+    int w = nes_ppu_render_w - sprite->x;
+    if (w > 8) w = 8;
+
+    back += sprite->x;
+
+    for (int x = 0; x < w; ++x) {
+        int pal_idx = (sprite->attr & oam_Attr_Flip_X) ?
+                      (((hi & 1) << 1) | (lo & 1)) :
+                      ( ((hi & 0x80) >> 6) |
+                        ((lo & 0x80) >> 7));
+        if (    hit_pos < 0 &&
+                pal_idx &&
+                *back != 0xFFU ) {
+            hit_pos = x + sprite->x;
+            break;
+        }
+        ++back;
+        if (sprite->attr & oam_Attr_Flip_X) {
+            hi >>= 1;
+            lo >>= 1;
+        } else {
+            hi <<= 1;
+            lo <<= 1;
+        }
+    }
+
+    return hit_pos;
+}
+
+
 static const SDL_Rect sprite_rect = {
     .x = 0,
     .y = 0,
@@ -322,7 +418,7 @@ static void render_sprites(nes_ppu* ppu,
         Render_Mode mode = (sprite->attr & oam_Attr_Background) ?
                            Render_Mode_Behind :
                            Render_Mode_Sprite;
-        if (i_sprite == 0) mode |= Render_Mode_Collide;
+//        if (i_sprite == 0) mode |= Render_Mode_Collide;
         if (sprite->attr & oam_Attr_Flip_X) {
             mode |= Render_Mode_Flip_X;
         }
@@ -349,54 +445,102 @@ static void render_sprites(nes_ppu* ppu,
 }
 
 static int sdl_render(nes_Renderer* rend, nes_ppu* ppu) {
+    int status = 0;
     sdl_render_data* data = (sdl_render_data*)rend->data;
 
-    // Emulate the happy part of the backdrop override quirk
-    int pal_idx = (ppu->addr >= nes_ppu_mem_pal_start) ?
-                  (ppu->addr & (nes_ppu_mem_pal_size - 1)) : 0;
-    SDL_Color ext = nes_palette[ppu->palette[pal_idx]];
-    SDL_FillRect(data->target, NULL,
-                 ((int)ext.r << 16) | ((int)ext.g << 8) | ext.b);
-    if (ppu->mask & ppu_Mask_Back) {
-        // TODO: Only render visible parts of background
-        render_background(ppu, 0, data->background->pixels,
-                          data->background->pitch);
-
-        int scroll_x = 0; //ppu->scroll_x;
-
-        SDL_Rect back_rect = {
-            .x = scroll_x,
-            .y = 0,
-            .w = nes_ppu_render_w - scroll_x,
-            .h = nes_ppu_render_h,
-        };
+    int line = (ppu->scanline - nes_ppu_prerender) / 8U;
+
+    printf("Scanline %3d -> Line %2d @ X %d\n",
+           ppu->scanline, line, ppu->scroll_x);
+
+    if (ppu->scanline < nes_ppu_prerender) {
+        // Emulate the happy part of the backdrop override quirk
+        int pal_idx = (ppu->addr >= nes_ppu_mem_pal_start) ?
+                      (ppu->addr & (nes_ppu_mem_pal_size - 1)) : 0;
+        SDL_Color ext = nes_palette[ppu->palette[pal_idx]];
+        SDL_FillRect(data->target, NULL,
+                     ((int)ext.r << 16) | ((int)ext.g << 8) | ext.b);
+
+    } else if (ppu->scanline < nes_ppu_prerender +
+                               nes_ppu_height) {
+        if (ppu->mask & ppu_Mask_Back) {
+            // TODO: Only re-render background if VRAM/scroll changes
+            render_background_line(ppu, line,
+                                   data->background->pixels,
+                                   data->background->pitch);
+
+            // Check for Sprite 0 Hit
+            // TODO: Account for fine X scroll
+            oam_sprite* sprite = (oam_sprite*)ppu->oam;
+            int bank = (ppu->control & ppu_Control_Sprite_Bank) ?
+                0x100 : 0;
+            int index = bank + sprite->index;
+            uint8_t* chr = &ppu->chr_mem[index * 16U];
+            int sprite_line = ppu->scanline - 2;
+            if (    ppu->hit_dot == 0 &&
+                    sprite->y + 7 >= sprite_line &&
+                    sprite->y - 7 <= sprite_line) {
+                int hit = -1;
+                uint8_t* back = data->background->pixels;
+                back += 8U * line * data->background->pitch;
+                for (int y = 0; y < 8; ++y) {
+                    hit = eval_sprite_line(
+                            ppu, ppu->scanline + y,
+                            sprite, chr, back
+                        );
+                    if (hit >= 0) {
+                        ppu->hit_line = ppu->scanline + y;
+                        ppu->hit_dot = hit;
+                        break;
+                    }
+                    back += data->background->pitch;
+                }
+            }
+        }
 
-        SDL_Rect render_rect = {
-            .x = 0,
-            .y = 0,
-            .w = nes_ppu_render_w - scroll_x,
-            .h = nes_ppu_render_h,
-        };
+    } else {
+        if (ppu->mask & ppu_Mask_Back) {
+            int scroll_x = 0; //ppu->scroll_x;
+
+            SDL_Rect back_rect = {
+                .x = scroll_x,
+                .y = 0,
+                .w = nes_ppu_render_w - scroll_x,
+                .h = nes_ppu_render_h,
+            };
+
+            SDL_Rect render_rect = {
+                .x = 0,
+                .y = 0,
+                .w = nes_ppu_render_w - scroll_x,
+                .h = nes_ppu_render_h,
+            };
+
+            SDL_BlitSurface(data->background, &back_rect,
+                            data->target, &render_rect);
+        }
+        if (ppu->mask & ppu_Mask_Sprite) {
+            render_sprites(ppu, data->sprite8, data->target,
+                           data->background->pixels,
+                           data->background->pitch);
+        }
+        SDL_Texture* texture = SDL_CreateTextureFromSurface(
+                data->renderer, data->target
+            );
+        SDL_RenderCopy(data->renderer, texture, NULL, NULL);
+        SDL_RenderPresent(data->renderer);
+        SDL_DestroyTexture(texture);
 
-        SDL_BlitSurface(data->background, &back_rect,
-                        data->target, &render_rect);
-    }
-    if (ppu->mask & ppu_Mask_Sprite) {
-        render_sprites(ppu, data->sprite8, data->target,
-                       data->background->pixels,
-                       data->background->pitch);
+        status = 1;
     }
-    SDL_Texture* texture = SDL_CreateTextureFromSurface(
-            data->renderer, data->target
-        );
-    SDL_RenderCopy(data->renderer, texture, NULL, NULL);
-    SDL_RenderPresent(data->renderer);
-    SDL_DestroyTexture(texture);
 
     // TODO: Handle this in the input loop, or anywhere else
     SDL_Event event = {0};
-    return (1 == SDL_PollEvent(&event) && event.type == SDL_QUIT) ?
-           -1 : 0;
+    if (1 == SDL_PollEvent(&event) && event.type == SDL_QUIT) {
+        status = -1;
+    }
+
+    return status;
 }