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Implement face culling modes

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This commit is contained in:
Luke Benstead 2021-04-07 15:13:17 +01:00
parent 43dc1023d6
commit 43e9508f6a
1 changed files with 41 additions and 6 deletions
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45
GL/platforms/software.c
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@ -14,6 +14,9 @@ static Matrix4x4 MATRIX;
static SDL_Window* WINDOW = NULL; static SDL_Window* WINDOW = NULL;
static SDL_Renderer* RENDERER = NULL; static SDL_Renderer* RENDERER = NULL;
GPUCulling CULL_MODE = GPU_CULLING_CCW;
static VideoMode vid_mode = { static VideoMode vid_mode = {
640, 480 640, 480
}; };
@ -33,7 +36,7 @@ typedef struct GPUVertex {
#define MIN(x, y) ((x) < (y) ? (x) : (y)) #define MIN(x, y) ((x) < (y) ? (x) : (y))
#define MAX(x, y) ((x) > (y) ? (x) : (y)) #define MAX(x, y) ((x) > (y) ? (x) : (y))
static void DrawTriangle(const GPUVertex* v0, const GPUVertex* v1, const GPUVertex* v2) { static void DrawTriangle(GPUVertex* v0, GPUVertex* v1, GPUVertex* v2) {
// Compute triangle bounding box. // Compute triangle bounding box.
int minX = MIN(MIN(v0->x, v1->x), v2->x); int minX = MIN(MIN(v0->x, v1->x), v2->x);
@ -57,10 +60,36 @@ static void DrawTriangle(const GPUVertex* v0, const GPUVertex* v1, const GPUVert
float area = 0.5 * (e0.c + e1.c + e2.c); float area = 0.5 * (e0.c + e1.c + e2.c);
/* This is very ugly. I don't understand the math properly
* so I just swap the vertex order if something is back-facing
* and we want to render it. Patches welcome! */
#define REVERSE_WINDING() \
GPUVertex* tv = v0; \
v0 = v1; \
v1 = tv; \
EdgeEquationInit(&e0, &v0->x, &v1->x); \
EdgeEquationInit(&e1, &v1->x, &v2->x); \
EdgeEquationInit(&e2, &v2->x, &v0->x); \
area = 0.5f * (e0.c + e1.c + e2.c) \
// Check if triangle is backfacing. // Check if triangle is backfacing.
if (area < 0) { if(CULL_MODE == GPU_CULLING_CCW) {
if(area < 0) {
return; return;
} }
} else if(CULL_MODE == GPU_CULLING_CW) {
if(area < 0) {
// We only draw front-facing polygons, so swap
// the back to front and draw
REVERSE_WINDING();
} else {
// Front facing, so bail
return;
}
} else if(area < 0) {
/* We're not culling, but this is backfacing, so swap vertices and edges */
REVERSE_WINDING();
}
ParameterEquation r, g, b; ParameterEquation r, g, b;
@ -116,6 +145,12 @@ void SceneListSubmit(void* src, int n) {
for(int i = 0; i < n; ++i, flags += step) { for(int i = 0; i < n; ++i, flags += step) {
if((*flags & GPU_CMD_POLYHDR) == GPU_CMD_POLYHDR) { if((*flags & GPU_CMD_POLYHDR) == GPU_CMD_POLYHDR) {
vertex_counter = 0; vertex_counter = 0;
uint32_t mode1 = *(flags + 1);
// Extract culling mode
uint32_t mask = mode1 & GPU_TA_PM1_CULLING_MASK;
CULL_MODE = mask >> GPU_TA_PM1_CULLING_SHIFT;
} else { } else {
switch(*flags) { switch(*flags) {
case GPU_CMD_VERTEX_EOL: case GPU_CMD_VERTEX_EOL:
@ -128,9 +163,9 @@ void SceneListSubmit(void* src, int n) {
} }
if(vertex_counter > 2) { if(vertex_counter > 2) {
const GPUVertex* v0 = (const GPUVertex*) (flags - step - step); GPUVertex* v0 = (GPUVertex*) (flags - step - step);
const GPUVertex* v1 = (const GPUVertex*) (flags - step); GPUVertex* v1 = (GPUVertex*) (flags - step);
const GPUVertex* v2 = (const GPUVertex*) (flags); GPUVertex* v2 = (GPUVertex*) (flags);
(vertex_counter % 2 == 0) ? DrawTriangle(v0, v1, v2) : DrawTriangle(v1, v0, v2); (vertex_counter % 2 == 0) ? DrawTriangle(v0, v1, v2) : DrawTriangle(v1, v0, v2);
} }