Add software renderer implementation

src/render/software/SDL_render_sw.c

@@ -33,6 +33,7 @@
 #include "SDL_drawline.h"
 #include "SDL_drawpoint.h"
 #include "SDL_rotate.h"
+#include "SDL_triangle.h"
 
 /* SDL surface based renderer implementation */
 
@@ -560,6 +561,71 @@ SW_RenderCopyEx(SDL_Renderer * renderer, SDL_Surface *surface, SDL_Texture * tex
     return retval;
 }
 
+
+typedef struct GeometryFillData
+{
+    SDL_Point dst;
+    SDL_Color color;
+} GeometryFillData;
+
+typedef struct GeometryCopyData
+{
+    SDL_Point src;
+    SDL_Point dst;
+    SDL_Color color;
+} GeometryCopyData;
+
+static int
+SW_QueueGeometry(SDL_Renderer *renderer, SDL_RenderCommand *cmd, SDL_Texture *texture,
+        SDL_Vertex *vertices, int num_vertices, int *indices, int num_indices, float scale_x, float scale_y)
+{
+    int i;
+    int count = indices ? num_indices : num_vertices;
+    void *verts;
+    int sz = texture ? sizeof (GeometryCopyData) : sizeof (GeometryFillData);
+
+    verts = (void *) SDL_AllocateRenderVertices(renderer, count * sz, 0, &cmd->data.draw.first);
+    if (!verts) {
+        return -1;
+    }
+
+    cmd->data.draw.count = count;
+
+    if (texture) {
+        GeometryCopyData *ptr = (GeometryCopyData *) verts;
+        for (i = 0; i < count; i++) {
+            SDL_Vertex *v = &vertices[indices ? indices[i] : i];
+
+            ptr->src.x = v->tex_coord.x;
+            ptr->src.y = v->tex_coord.y;
+
+            ptr->dst.x = v->position.x * scale_x + renderer->viewport.x;
+            ptr->dst.y = v->position.y * scale_y + renderer->viewport.y;
+            trianglepoint_2_fixedpoint(&ptr->dst);
+
+            ptr->color = v->color;
+
+            ptr++;
+       }
+    } else {
+        GeometryFillData *ptr = (GeometryFillData *) verts;
+
+        for (i = 0; i < count; i++) {
+            SDL_Vertex *v = &vertices[indices ? indices[i] : i];
+
+            ptr->dst.x = v->position.x * scale_x + renderer->viewport.x;
+            ptr->dst.y = v->position.y * scale_y + renderer->viewport.y;
+            trianglepoint_2_fixedpoint(&ptr->dst);
+
+            ptr->color = v->color;
+
+            ptr++;
+       }
+    }
+
+    return 0;
+}
+
 static void
 PrepTextureForCopy(const SDL_RenderCommand *cmd)
 {
@@ -734,6 +800,39 @@ SW_RunCommandQueue(SDL_Renderer * renderer, SDL_RenderCommand *cmd, void *vertic
                 break;
             }
 
+            case SDL_RENDERCMD_GEOMETRY: {
+                int i;
+                SDL_Rect *verts = (SDL_Rect *) (((Uint8 *) vertices) + cmd->data.draw.first);
+                const int count = (int) cmd->data.draw.count;
+                SDL_Texture *texture = cmd->data.draw.texture;
+                const SDL_BlendMode blend = cmd->data.draw.blend;
+
+                SetDrawState(surface, &drawstate);
+
+                if (texture) {
+                    SDL_Surface *src = (SDL_Surface *) texture->driverdata;
+
+                    GeometryCopyData *ptr = (GeometryCopyData *) verts;
+
+                    PrepTextureForCopy(cmd);
+                    for (i = 0; i < count; i += 3, ptr += 3) {
+                        SDL_SW_BlitTriangle(
+                                src,
+                                &(ptr[0].src), &(ptr[1].src), &(ptr[2].src),
+                                surface,
+                                &(ptr[0].dst), &(ptr[1].dst), &(ptr[2].dst),
+                                ptr[0].color, ptr[1].color, ptr[2].color);
+                    }
+                } else {
+                    GeometryFillData *ptr = (GeometryFillData *) verts;
+                    for (i = 0; i < count; i += 3, ptr += 3) {
+                        SDL_SW_FillTriangle(surface, &(ptr[0].dst), &(ptr[1].dst), &(ptr[2].dst), blend, ptr[0].color, ptr[1].color, ptr[2].color);
+                    }
+                }
+
+                break;
+            }
+
             case SDL_RENDERCMD_NO_OP:
                 break;
         }
@@ -843,6 +942,7 @@ SW_CreateRendererForSurface(SDL_Surface * surface)
     renderer->QueueFillRects = SW_QueueFillRects;
     renderer->QueueCopy = SW_QueueCopy;
     renderer->QueueCopyEx = SW_QueueCopyEx;
+    renderer->QueueGeometry = SW_QueueGeometry;
     renderer->RunCommandQueue = SW_RunCommandQueue;
     renderer->RenderReadPixels = SW_RenderReadPixels;
     renderer->RenderPresent = SW_RenderPresent;

src/render/software/SDL_triangle.c

@@ -0,0 +1,827 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2021 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "../../SDL_internal.h"
+
+#if SDL_VIDEO_RENDER_SW && !SDL_RENDER_DISABLED
+
+#include "SDL_surface.h"
+#include "SDL_triangle.h"
+
+#include "../../video/SDL_blit.h"
+
+/* fixed points bits precision
+ * Set to 1, so that it can start rendering wth middle of a pixel precision.
+ * It doesn't need to be increased.
+ * But, if increased too much, it overflows (srcx, srcy) coordinates used for filling with texture.
+ * (which could be turned to int64).
+ */
+#define FP_BITS   1
+
+
+#define COLOR_EQ(c1, c2)    ((c1).r == (c2).r && (c1).g == (c2).g && (c1).b == (c2).b && (c1).a == (c2).a)
+
+static void SDL_BlitTriangle_Slow(SDL_BlitInfo * info,
+        SDL_Point s2_x_area, SDL_Rect dstrect, int area, int bias_w0, int bias_w1, int bias_w2,
+    int d2d1_y, int d1d2_x, int d0d2_y, int d2d0_x, int d1d0_y, int d0d1_x,
+    int s2s0_x, int s2s1_x, int s2s0_y, int s2s1_y, int w0_row, int w1_row, int w2_row,
+    SDL_Color c0, SDL_Color c1, SDL_Color c2, int is_uniform);
+
+#if 0
+int SDL_BlitTriangle(SDL_Surface *src, const SDL_Point srcpoints[3], SDL_Surface *dst, const SDL_Point dstpoints[3])
+{
+    int i;
+    SDL_Point points[6];
+
+    if (src == NULL || dst == NULL) {
+        return -1;
+    }
+
+    for (i = 0; i < 3; i++) {
+        if (srcpoints[i].x < 0 || srcpoints[i].y < 0 || srcpoints[i].x >= src->w || srcpoints[i].y >= src->h) {
+            return SDL_SetError("Values of 'srcpoints' out of bounds");
+        }
+    }
+
+    points[0] = srcpoints[0];
+    points[1] = dstpoints[0];
+    points[2] = srcpoints[1];
+    points[3] = dstpoints[1];
+    points[4] = srcpoints[2];
+    points[5] = dstpoints[2];
+    for (i = 0; i < 3; i++) {
+        trianglepoint_2_fixedpoint(&points[2 * i + 1]);
+    }
+    return SDL_SW_BlitTriangle(src, dst, points);
+}
+
+int SDL_FillTriangle(SDL_Surface *dst, const SDL_Point points[3], Uint32 color)
+{
+    int i;
+    SDL_Point points_tmp[3];
+    if (dst == NULL) {
+        return -1;
+    }
+    for (i = 0; i < 3; i++) {
+        points_tmp[i] = points[i];
+        trianglepoint_2_fixedpoint(&points_tmp[i]);
+    }
+    return SDL_SW_FillTriangle(dst, points_tmp, SDL_BLENDMODE_NONE, color);
+}
+#endif
+
+/* cross product AB x AC */
+static float cross_product(const SDL_Point *a, const SDL_Point *b, int c_x, int c_y)
+{
+    return (b->x - a->x) * (c_y - a->y) - (b->y - a->y) * (c_x - a->x);
+}
+
+/* check for top left rules */
+static int is_top_left(const SDL_Point *a, const SDL_Point *b, int is_clockwise)
+{
+    if (is_clockwise) {
+        if (a->y == b->y && a->x < b->x) {
+            return 1;
+        }
+        if (b->y < a->y) {
+            return 1;
+        }
+    } else {
+        if (a->y == b->y && b->x < a->x) {
+            return 1;
+        }
+        if (a->y < b->y) {
+            return 1;
+        }
+    }
+    return 0;
+}
+
+void trianglepoint_2_fixedpoint(SDL_Point *a) {
+    a->x <<= FP_BITS;
+    a->y <<= FP_BITS;
+}
+
+/* bounding rect of three points */
+static void bounding_rect(const SDL_Point *a, const SDL_Point *b, const SDL_Point *c, SDL_Rect *r)
+{
+    int min_x = SDL_min(a->x, SDL_min(b->x, c->x));
+    int max_x = SDL_max(a->x, SDL_max(b->x, c->x));
+    int min_y = SDL_min(a->y, SDL_min(b->y, c->y));
+    int max_y = SDL_max(a->y, SDL_max(b->y, c->y));
+    /* points are in fixed point, shift back */
+    r->x = min_x >> FP_BITS;
+    r->y = min_y >> FP_BITS;
+    r->w = (max_x - min_x) >> FP_BITS;
+    r->h = (max_y - min_y) >> FP_BITS;
+}
+
+/* Triangle rendering, using Barycentric coordinates (w0, w1, w2)
+ *
+ * The cross product isn't computed from scratch at each iteration,
+ * but optimized using constant step increments
+ *
+ */
+
+#define TRIANGLE_BEGIN_LOOP                                                                             \
+    {                                                                                                   \
+        int x, y;                                                                                       \
+        for (y = 0; y < dstrect.h; y++) {                                                               \
+            /* y start */                                                                               \
+            int w0 = w0_row;                                                                            \
+            int w1 = w1_row;                                                                            \
+            int w2 = w2_row;                                                                            \
+            for (x = 0; x < dstrect.w; x++) {                                                           \
+                /* In triangle */                                                                       \
+                if (w0 + bias_w0 >= 0 && w1 + bias_w1 >= 0 && w2 + bias_w2 >= 0) {                      \
+                    Uint8 *dptr = (Uint8 *) dst_ptr + x * dstbpp;                                       \
+
+
+#define TRIANGLE_GET_TEXTCOORD                                                                          \
+                    int srcx = (w0 * s2s0_x + w1 * s2s1_x + s2_x_area.x) / area;                        \
+                    int srcy = (w0 * s2s0_y + w1 * s2s1_y + s2_x_area.y) / area;                        \
+
+#define TRIANGLE_GET_MAPPED_COLOR                                                                       \
+                    int r = (w0 * c0.r + w1 * c1.r + w2 * c2.r) / area;                                 \
+                    int g = (w0 * c0.g + w1 * c1.g + w2 * c2.g) / area;                                 \
+                    int b = (w0 * c0.b + w1 * c1.b + w2 * c2.b) / area;                                 \
+                    int a = (w0 * c0.a + w1 * c1.a + w2 * c2.a) / area;                                 \
+                    int color = SDL_MapRGBA(format, r, g, b, a);                                        \
+
+#define TRIANGLE_GET_COLOR                                                                              \
+                    int r = (w0 * c0.r + w1 * c1.r + w2 * c2.r) / area;                                 \
+                    int g = (w0 * c0.g + w1 * c1.g + w2 * c2.g) / area;                                 \
+                    int b = (w0 * c0.b + w1 * c1.b + w2 * c2.b) / area;                                 \
+                    int a = (w0 * c0.a + w1 * c1.a + w2 * c2.a) / area;                                 \
+
+
+#define TRIANGLE_END_LOOP                                                                               \
+                }                                                                                       \
+                /* x += 1 */                                                                            \
+                w0 += d2d1_y;                                                                           \
+                w1 += d0d2_y;                                                                           \
+                w2 += d1d0_y;                                                                           \
+            }                                                                                           \
+            /* y += 1 */                                                                                \
+            w0_row += d1d2_x;                                                                           \
+            w1_row += d2d0_x;                                                                           \
+            w2_row += d0d1_x;                                                                           \
+            dst_ptr += dst_pitch;                                                                       \
+        }                                                                                               \
+    }                                                                                                   \
+
+int SDL_SW_FillTriangle(SDL_Surface *dst, SDL_Point *d0, SDL_Point *d1, SDL_Point *d2, SDL_BlendMode blend, SDL_Color c0, SDL_Color c1, SDL_Color c2)
+{
+    int ret = 0;
+    int dst_locked = 0;
+
+    SDL_Rect dstrect;
+
+    int dstbpp;
+    Uint8 *dst_ptr;
+    int dst_pitch;
+
+    int area, is_clockwise;
+
+    int d2d1_y, d1d2_x, d0d2_y, d2d0_x, d1d0_y, d0d1_x;
+    int w0_row, w1_row, w2_row;
+    int bias_w0, bias_w1, bias_w2;
+
+    int is_uniform;
+
+    SDL_Surface *tmp = NULL;
+
+    if (dst == NULL) {
+        return -1;
+    }
+
+    area = cross_product(d0, d1, d2->x, d2->y);
+
+    is_uniform = COLOR_EQ(c0, c1) && COLOR_EQ(c1, c2);
+
+    /* Flat triangle */
+    if (area == 0) {
+        return 0;
+    }
+
+    /* Lock the destination, if needed */
+    if (SDL_MUSTLOCK(dst)) {
+        if (SDL_LockSurface(dst) < 0) {
+            ret = -1;
+            goto end;
+        } else {
+            dst_locked = 1;
+        }
+    }
+
+    bounding_rect(d0, d1, d2, &dstrect);
+
+    {
+        /* Clip triangle rect with surface rect */
+        SDL_Rect rect;
+        rect.x = 0;
+        rect.y = 0;
+        rect.w = dst->w;
+        rect.h = dst->h;
+        SDL_IntersectRect(&dstrect, &rect, &dstrect);
+    }
+
+    {
+        /* Clip triangle with surface clip rect */
+        SDL_Rect rect;
+        SDL_GetClipRect(dst, &rect);
+        SDL_IntersectRect(&dstrect, &rect, &dstrect);
+    }
+
+
+    if (blend != SDL_BLENDMODE_NONE) {
+        int format = dst->format->format;
+
+        /* need an alpha format */
+        if (! dst->format->Amask) {
+            format = SDL_PIXELFORMAT_ARGB8888;
+        }
+
+        /* Use an intermediate surface */
+        tmp = SDL_CreateRGBSurfaceWithFormat(0, dstrect.w, dstrect.h, 0, format);
+        if (tmp == NULL) {
+            ret = -1;
+            goto end;
+        }
+
+        if (blend == SDL_BLENDMODE_MOD) {
+            Uint32 c = SDL_MapRGBA(tmp->format, 255, 255, 255, 255);
+            SDL_FillRect(tmp, NULL, c);
+        }
+
+        SDL_SetSurfaceBlendMode(tmp, blend);
+
+        dstbpp = tmp->format->BytesPerPixel;
+        dst_ptr = tmp->pixels;
+        dst_pitch = tmp->pitch;
+
+    } else {
+        /* Write directly to destination surface */
+        dstbpp = dst->format->BytesPerPixel;
+        dst_ptr = (Uint8 *)dst->pixels + dstrect.x * dstbpp + dstrect.y * dst->pitch;
+        dst_pitch = dst->pitch;
+    }
+
+    is_clockwise = area > 0;
+    area = SDL_abs(area);
+
+    d2d1_y = (d1->y - d2->y) << FP_BITS;
+    d0d2_y = (d2->y - d0->y) << FP_BITS;
+    d1d0_y = (d0->y - d1->y) << FP_BITS;
+    d1d2_x = (d2->x - d1->x) << FP_BITS;
+    d2d0_x = (d0->x - d2->x) << FP_BITS;
+    d0d1_x = (d1->x - d0->x) << FP_BITS;
+
+    /* Starting point for rendering, at the middle of a pixel */
+    {
+        SDL_Point p;
+        p.x = dstrect.x;
+        p.y = dstrect.y;
+        trianglepoint_2_fixedpoint(&p);
+        p.x += (1 << FP_BITS) / 2;
+        p.y += (1 << FP_BITS) / 2;
+        w0_row = cross_product(d1, d2, p.x, p.y);
+        w1_row = cross_product(d2, d0, p.x, p.y);
+        w2_row = cross_product(d0, d1, p.x, p.y);
+    }
+
+    /* Handle anti-clockwise triangles */
+    if (! is_clockwise) {
+        d2d1_y *= -1;
+        d0d2_y *= -1;
+        d1d0_y *= -1;
+        d1d2_x *= -1;
+        d2d0_x *= -1;
+        d0d1_x *= -1;
+        w0_row *= -1;
+        w1_row *= -1;
+        w2_row *= -1;
+    }
+
+    /* Add a bias to respect top-left rasterization rule */
+    bias_w0 = (is_top_left(d1, d2, is_clockwise) ? 0 : -1);
+    bias_w1 = (is_top_left(d2, d0, is_clockwise) ? 0 : -1);
+    bias_w2 = (is_top_left(d0, d1, is_clockwise) ? 0 : -1);
+
+    if (is_uniform) {
+        Uint32 color;
+        if (tmp) {
+            if (dst->format->Amask) {
+                color = SDL_MapRGBA(tmp->format, c0.r, c0.g, c0.b, c0.a);
+            } else {
+                //color = SDL_MapRGB(tmp->format, c0.r, c0.g, c0.b);
+                color = SDL_MapRGBA(tmp->format, c0.r, c0.g, c0.b, c0.a);
+            }
+        } else {
+            color = SDL_MapRGBA(dst->format, c0.r, c0.g, c0.b, c0.a);
+        }
+
+        if (dstbpp == 4) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                *(Uint32 *)dptr = color;
+            }
+            TRIANGLE_END_LOOP
+        } else if (dstbpp == 3) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                Uint8 *s = (Uint8*)&color;
+                dptr[0] = s[0];
+                dptr[1] = s[1];
+                dptr[2] = s[2];
+            }
+            TRIANGLE_END_LOOP
+        } else if (dstbpp == 2) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                *(Uint16 *)dptr = color;
+            }
+            TRIANGLE_END_LOOP
+        } else if (dstbpp == 1) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                *dptr = color;
+            }
+            TRIANGLE_END_LOOP
+        }
+    } else {
+        SDL_PixelFormat *format = dst->format;
+        if (tmp) {
+            format = tmp->format;
+        }
+        if (dstbpp == 4) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                TRIANGLE_GET_MAPPED_COLOR
+                *(Uint32 *)dptr = color;
+            }
+            TRIANGLE_END_LOOP
+        } else if (dstbpp == 3) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                TRIANGLE_GET_MAPPED_COLOR
+                Uint8 *s = (Uint8*)&color;
+                dptr[0] = s[0];
+                dptr[1] = s[1];
+                dptr[2] = s[2];
+            }
+            TRIANGLE_END_LOOP
+        } else if (dstbpp == 2) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                TRIANGLE_GET_MAPPED_COLOR
+                *(Uint16 *)dptr = color;
+            }
+            TRIANGLE_END_LOOP
+        } else if (dstbpp == 1) {
+            TRIANGLE_BEGIN_LOOP
+            {
+                TRIANGLE_GET_MAPPED_COLOR
+                *dptr = color;
+            }
+            TRIANGLE_END_LOOP
+        }
+    }
+
+    if (tmp) {
+        SDL_BlitSurface(tmp, NULL, dst, &dstrect);
+        SDL_FreeSurface(tmp);
+    }
+
+end:
+    if (dst_locked) {
+        SDL_UnlockSurface(dst);
+    }
+
+    return ret;
+}
+
+
+
+
+
+
+
+int SDL_SW_BlitTriangle(
+        SDL_Surface *src,
+        SDL_Point *s0, SDL_Point *s1, SDL_Point *s2,
+        SDL_Surface *dst,
+        SDL_Point *d0, SDL_Point *d1, SDL_Point *d2,
+        SDL_Color c0, SDL_Color c1, SDL_Color c2)
+{
+    int ret = 0;
+    int src_locked = 0;
+    int dst_locked = 0;
+
+    SDL_BlendMode blend;
+
+    SDL_Rect srcrect;
+    SDL_Rect dstrect;
+
+    SDL_Point s2_x_area;
+
+    int dstbpp;
+    Uint8 *dst_ptr;
+    int dst_pitch;
+
+    int *src_ptr;
+    int src_pitch;
+
+    int area, is_clockwise;
+
+    int d2d1_y, d1d2_x, d0d2_y, d2d0_x, d1d0_y, d0d1_x;
+    int s2s0_x, s2s1_x, s2s0_y, s2s1_y;
+
+    int w0_row, w1_row, w2_row;
+    int bias_w0, bias_w1, bias_w2;
+
+    int is_uniform;
+
+    int has_modulation;
+
+    if (src == NULL || dst == NULL) {
+        return -1;
+    }
+
+    area = cross_product(d0, d1, d2->x, d2->y);
+
+    /* Flat triangle */
+    if (area == 0) {
+        return 0;
+    }
+
+    /* Lock the destination, if needed */
+    if (SDL_MUSTLOCK(dst)) {
+        if (SDL_LockSurface(dst) < 0) {
+            ret = -1;
+            goto end;
+        } else {
+            dst_locked = 1;
+        }
+    }
+
+    /* Lock the source, if needed */
+    if (SDL_MUSTLOCK(src)) {
+        if (SDL_LockSurface(src) < 0) {
+            ret = -1;
+            goto end;
+        } else {
+            src_locked = 1;
+        }
+    }
+
+    is_uniform = COLOR_EQ(c0, c1) && COLOR_EQ(c1, c2);
+
+    bounding_rect(s0, s1, s2, &srcrect);
+    bounding_rect(d0, d1, d2, &dstrect);
+
+    SDL_GetSurfaceBlendMode(src, &blend);
+
+    if (is_uniform) {
+        // SDL_GetSurfaceColorMod(src, &r, &g, &b);
+        has_modulation = c0.r != 255 || c0.g != 255 || c0.b != 255 || c0.a != 255;;
+    } else {
+        has_modulation = SDL_TRUE;
+    }
+
+    {
+        /* Clip triangle rect with surface rect */
+        SDL_Rect rect;
+        rect.x = 0;
+        rect.y = 0;
+        rect.w = dst->w;
+        rect.h = dst->h;
+
+        SDL_IntersectRect(&dstrect, &rect, &dstrect);
+    }
+
+    {
+        /* Clip triangle with surface clip rect */
+        SDL_Rect rect;
+        SDL_GetClipRect(dst, &rect);
+        SDL_IntersectRect(&dstrect, &rect, &dstrect);
+    }
+
+    /* Set destination pointer */
+    dstbpp = dst->format->BytesPerPixel;
+    dst_ptr = (Uint8 *)dst->pixels + dstrect.x * dstbpp + dstrect.y * dst->pitch;
+    dst_pitch = dst->pitch;
+
+    /* Set source pointer */
+    src_ptr = src->pixels;
+    src_pitch = src->pitch;
+
+    is_clockwise = area > 0;
+    area = SDL_abs(area);
+
+    d2d1_y = (d1->y - d2->y) << FP_BITS;
+    d0d2_y = (d2->y - d0->y) << FP_BITS;
+    d1d0_y = (d0->y - d1->y) << FP_BITS;
+
+
+    d1d2_x = (d2->x - d1->x) << FP_BITS;
+    d2d0_x = (d0->x - d2->x) << FP_BITS;
+    d0d1_x = (d1->x - d0->x) << FP_BITS;
+
+    s2s0_x = s0->x - s2->x;
+    s2s1_x = s1->x - s2->x;
+    s2s0_y = s0->y - s2->y;
+    s2s1_y = s1->y - s2->y;
+
+    /* Starting point for rendering, at the middle of a pixel */
+    {
+        SDL_Point p;
+        p.x = dstrect.x;
+        p.y = dstrect.y;
+        trianglepoint_2_fixedpoint(&p);
+        p.x += (1 << FP_BITS) / 2;
+        p.y += (1 << FP_BITS) / 2;
+        w0_row = cross_product(d1, d2, p.x, p.y);
+        w1_row = cross_product(d2, d0, p.x, p.y);
+        w2_row = cross_product(d0, d1, p.x, p.y);
+    }
+
+    /* Handle anti-clockwise triangles */
+    if (! is_clockwise) {
+        d2d1_y *= -1;
+        d0d2_y *= -1;
+        d1d0_y *= -1;
+        d1d2_x *= -1;
+        d2d0_x *= -1;
+        d0d1_x *= -1;
+        w0_row *= -1;
+        w1_row *= -1;
+        w2_row *= -1;
+    }
+
+    /* Add a bias to respect top-left rasterization rule */
+    bias_w0 = (is_top_left(d1, d2, is_clockwise) ? 0 : -1);
+    bias_w1 = (is_top_left(d2, d0, is_clockwise) ? 0 : -1);
+    bias_w2 = (is_top_left(d0, d1, is_clockwise) ? 0 : -1);
+
+    /* precompute constant 's2->x * area' used in TRIANGLE_GET_TEXTCOORD */
+    s2_x_area.x = s2->x * area;
+    s2_x_area.y = s2->y * area;
+
+    if (blend != SDL_BLENDMODE_NONE || src->format->format != dst->format->format || has_modulation || ! is_uniform) {
+        /* Use SDL_BlitTriangle_Slow */
+
+        SDL_BlitInfo *info = &src->map->info;
+        SDL_BlitInfo tmp_info;
+
+        SDL_zero(tmp_info);
+
+        tmp_info.src_fmt = src->format;
+        tmp_info.dst_fmt = dst->format;
+        tmp_info.flags = info->flags;
+        /*
+        tmp_info.r = info->r;
+        tmp_info.g = info->g;
+        tmp_info.b = info->b;
+        tmp_info.a = info->a;
+        */
+        tmp_info.r = c0.r;
+        tmp_info.g = c0.g;
+        tmp_info.b = c0.b;
+        tmp_info.a = c0.a;
+
+
+        tmp_info.flags &= ~(SDL_COPY_MODULATE_COLOR | SDL_COPY_MODULATE_ALPHA);
+
+        if (c0.r != 255  || c1.r != 255 || c2.r != 255 ||
+                c0.g != 255  || c1.g != 255 || c2.g != 255 ||
+                c0.b != 255  || c1.b != 255 || c2.b != 255) {
+            tmp_info.flags |= SDL_COPY_MODULATE_COLOR;
+        }
+
+        if (c0.a != 255 || c1.a != 255 || c2.a != 255) {
+            tmp_info.flags |= SDL_COPY_MODULATE_ALPHA;
+        }
+
+        tmp_info.colorkey = info->colorkey;
+
+        /* src */
+        tmp_info.src = (Uint8 *) src_ptr;
+        tmp_info.src_pitch = src_pitch;
+
+        /* dst */
+        tmp_info.dst = (Uint8 *) dst_ptr;
+        tmp_info.dst_pitch = dst_pitch;
+
+        SDL_BlitTriangle_Slow(&tmp_info, s2_x_area, dstrect, area, bias_w0, bias_w1, bias_w2,
+                d2d1_y, d1d2_x, d0d2_y, d2d0_x, d1d0_y, d0d1_x,
+                s2s0_x, s2s1_x, s2s0_y, s2s1_y, w0_row, w1_row, w2_row,
+                c0, c1, c2, is_uniform);
+
+        goto end;
+    }
+
+    if (dstbpp == 4) {
+        TRIANGLE_BEGIN_LOOP
+        {
+            TRIANGLE_GET_TEXTCOORD
+            Uint32 *sptr = (Uint32 *)((Uint8 *) src_ptr + srcy * src_pitch);
+            *(Uint32 *)dptr = sptr[srcx];
+        }
+        TRIANGLE_END_LOOP
+    } else if (dstbpp == 3) {
+        TRIANGLE_BEGIN_LOOP
+        {
+            TRIANGLE_GET_TEXTCOORD
+            Uint8 *sptr = (Uint8 *)((Uint8 *) src_ptr + srcy * src_pitch);
+            dptr[0] = sptr[3 * srcx];
+            dptr[1] = sptr[3 * srcx + 1];
+            dptr[2] = sptr[3 * srcx + 2];
+        }
+        TRIANGLE_END_LOOP
+    } else if (dstbpp == 2) {
+        TRIANGLE_BEGIN_LOOP
+        {
+            TRIANGLE_GET_TEXTCOORD
+            Uint16 *sptr = (Uint16 *)((Uint8 *) src_ptr + srcy * src_pitch);
+            *(Uint16 *)dptr = sptr[srcx];
+        }
+        TRIANGLE_END_LOOP
+    } else if (dstbpp == 1) {
+        TRIANGLE_BEGIN_LOOP
+        {
+            TRIANGLE_GET_TEXTCOORD
+            Uint8 *sptr = (Uint8 *)((Uint8 *) src_ptr + srcy * src_pitch);
+            *dptr = sptr[srcx];
+        }
+        TRIANGLE_END_LOOP
+    }
+
+end:
+    if (dst_locked) {
+        SDL_UnlockSurface(dst);
+    }
+    if (src_locked) {
+        SDL_UnlockSurface(src);
+    }
+
+    return ret;
+}
+
+
+static void
+SDL_BlitTriangle_Slow(SDL_BlitInfo *info,
+        SDL_Point s2_x_area, SDL_Rect dstrect, int area, int bias_w0, int bias_w1, int bias_w2,
+    int d2d1_y, int d1d2_x, int d0d2_y, int d2d0_x, int d1d0_y, int d0d1_x,
+    int s2s0_x, int s2s1_x, int s2s0_y, int s2s1_y, int w0_row, int w1_row, int w2_row,
+    SDL_Color c0, SDL_Color c1, SDL_Color c2, int is_uniform)
+{
+    const int flags = info->flags;
+    Uint32 modulateR = info->r;
+    Uint32 modulateG = info->g;
+    Uint32 modulateB = info->b;
+    Uint32 modulateA = info->a;
+    Uint32 srcpixel;
+    Uint32 srcR, srcG, srcB, srcA;
+    Uint32 dstpixel;
+    Uint32 dstR, dstG, dstB, dstA;
+    SDL_PixelFormat *src_fmt = info->src_fmt;
+    SDL_PixelFormat *dst_fmt = info->dst_fmt;
+    int srcbpp = src_fmt->BytesPerPixel;
+    int dstbpp = dst_fmt->BytesPerPixel;
+    Uint32 rgbmask = ~src_fmt->Amask;
+    Uint32 ckey = info->colorkey & rgbmask;
+
+    Uint8 *dst_ptr = info->dst;
+    int dst_pitch = info->dst_pitch;;
+
+    TRIANGLE_BEGIN_LOOP
+    {
+        Uint8 *src;
+        Uint8 *dst = dptr;
+        TRIANGLE_GET_TEXTCOORD
+        src = (info->src + (srcy * info->src_pitch) + (srcx * srcbpp));
+        if (src_fmt->Amask) {
+            DISEMBLE_RGBA(src, srcbpp, src_fmt, srcpixel, srcR, srcG,
+                          srcB, srcA);
+        } else {
+            DISEMBLE_RGB(src, srcbpp, src_fmt, srcpixel, srcR, srcG,
+                         srcB);
+            srcA = 0xFF;
+        }
+        if (flags & SDL_COPY_COLORKEY) {
+            /* srcpixel isn't set for 24 bpp */
+            if (srcbpp == 3) {
+                srcpixel = (srcR << src_fmt->Rshift) |
+                    (srcG << src_fmt->Gshift) | (srcB << src_fmt->Bshift);
+            }
+            if ((srcpixel & rgbmask) == ckey) {
+                continue;
+            }
+        }
+        if (dst_fmt->Amask) {
+            DISEMBLE_RGBA(dst, dstbpp, dst_fmt, dstpixel, dstR, dstG,
+                          dstB, dstA);
+        } else {
+            DISEMBLE_RGB(dst, dstbpp, dst_fmt, dstpixel, dstR, dstG,
+                         dstB);
+            dstA = 0xFF;
+        }
+
+        if (! is_uniform) {
+            TRIANGLE_GET_COLOR
+            modulateR = r;
+            modulateG = g;
+            modulateB = b;
+            modulateA = a;
+        }
+
+        if (flags & SDL_COPY_MODULATE_COLOR) {
+            srcR = (srcR * modulateR) / 255;
+            srcG = (srcG * modulateG) / 255;
+            srcB = (srcB * modulateB) / 255;
+        }
+        if (flags & SDL_COPY_MODULATE_ALPHA) {
+            srcA = (srcA * modulateA) / 255;
+        }
+        if (flags & (SDL_COPY_BLEND | SDL_COPY_ADD)) {
+            /* This goes away if we ever use premultiplied alpha */
+            if (srcA < 255) {
+                srcR = (srcR * srcA) / 255;
+                srcG = (srcG * srcA) / 255;
+                srcB = (srcB * srcA) / 255;
+            }
+        }
+        switch (flags & (SDL_COPY_BLEND | SDL_COPY_ADD | SDL_COPY_MOD | SDL_COPY_MUL)) {
+        case 0:
+            dstR = srcR;
+            dstG = srcG;
+            dstB = srcB;
+            dstA = srcA;
+            break;
+        case SDL_COPY_BLEND:
+            dstR = srcR + ((255 - srcA) * dstR) / 255;
+            dstG = srcG + ((255 - srcA) * dstG) / 255;
+            dstB = srcB + ((255 - srcA) * dstB) / 255;
+            dstA = srcA + ((255 - srcA) * dstA) / 255;
+            break;
+        case SDL_COPY_ADD:
+            dstR = srcR + dstR;
+            if (dstR > 255)
+                dstR = 255;
+            dstG = srcG + dstG;
+            if (dstG > 255)
+                dstG = 255;
+            dstB = srcB + dstB;
+            if (dstB > 255)
+                dstB = 255;
+            break;
+        case SDL_COPY_MOD:
+            dstR = (srcR * dstR) / 255;
+            dstG = (srcG * dstG) / 255;
+            dstB = (srcB * dstB) / 255;
+            break;
+        case SDL_COPY_MUL:
+            dstR = ((srcR * dstR) + (dstR * (255 - srcA))) / 255;
+            if (dstR > 255)
+                dstR = 255;
+            dstG = ((srcG * dstG) + (dstG * (255 - srcA))) / 255;
+            if (dstG > 255)
+                dstG = 255;
+            dstB = ((srcB * dstB) + (dstB * (255 - srcA))) / 255;
+            if (dstB > 255)
+                dstB = 255;
+            dstA = ((srcA * dstA) + (dstA * (255 - srcA))) / 255;
+            if (dstA > 255)
+                dstA = 255;
+            break;
+        }
+        if (dst_fmt->Amask) {
+            ASSEMBLE_RGBA(dst, dstbpp, dst_fmt, dstR, dstG, dstB, dstA);
+        } else {
+            ASSEMBLE_RGB(dst, dstbpp, dst_fmt, dstR, dstG, dstB);
+        }
+    }
+    TRIANGLE_END_LOOP
+}
+
+#endif /* SDL_VIDEO_RENDER_SW && !SDL_RENDER_DISABLED */
+
+/* vi: set ts=4 sw=4 expandtab: */

src/render/software/SDL_triangle.h

@@ -0,0 +1,42 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2021 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+#ifndef SDL_triangle_h_
+#define SDL_triangle_h_
+
+#include "../../SDL_internal.h"
+
+extern int SDL_SW_FillTriangle(SDL_Surface *dst,
+        SDL_Point *d0, SDL_Point *d1, SDL_Point *d2,
+        SDL_BlendMode blend, SDL_Color c0, SDL_Color c1, SDL_Color c2);
+
+extern int SDL_SW_BlitTriangle(
+        SDL_Surface *src,
+        SDL_Point *s0, SDL_Point *s1, SDL_Point *s2,
+        SDL_Surface *dst,
+        SDL_Point *d0, SDL_Point *d1, SDL_Point *d2,
+        SDL_Color c0, SDL_Color c1, SDL_Color c2);
+
+extern void trianglepoint_2_fixedpoint(SDL_Point *a);
+
+#endif /* SDL_triangle_h_ */
+
+/* vi: set ts=4 sw=4 expandtab: */