glReadPixels(): support reading the stencil buffer

Tested with readpixels.cpp: https://github.com/mardy/freeglut/blob/with-tutorials/tutorials/readpixels.cpp
mardy · Oct 24, 2024 · 785b33a · 785b33a
1 parent 70f3c13
commit 785b33a
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Showing 5 changed files with 69 additions and 18 deletions.
diff --git a/src/pixel_stream.cpp b/src/pixel_stream.cpp
@@ -60,5 +60,6 @@ const struct ComponentsPerFormat _ogx_pixels_components_per_format[] = {
     { GL_BLUE, 1, { 2 }},
     { GL_ALPHA, 1, { 3 }},
     { GL_DEPTH_COMPONENT, 1, {}},
+    { GL_STENCIL_INDEX, 1, { 0 }},
     { 0, }
 };
diff --git a/src/pixel_stream.h b/src/pixel_stream.h
@@ -358,4 +358,17 @@ struct DepthPixelStream: public GenericPixelStream<T> {
     }
 };
 
+template <typename T>
+struct StencilPixelStream: public GenericPixelStream<T> {
+    using GenericPixelStream<T>::GenericPixelStream;
+    using GenericPixelStream<T>::m_write_pos;
+
+    void write(GXColor color) override {
+        this->d()[m_write_pos++] = glcomponent<T>(color.r)
+            * (1 << glparamstate.transfer_index_shift)
+            + glparamstate.transfer_index_offset;
+        this->check_next_row();
+    }
+};
+
 #endif /* OPENGX_PIXEL_STREAM_H */
diff --git a/src/raster.cpp b/src/raster.cpp
@@ -35,6 +35,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "pixel_stream.h"
 #include "pixels.h"
 #include "state.h"
+#include "stencil.h"
 #include "texel.h"
 #include "utils.h"
 
@@ -355,6 +356,7 @@ struct TextureReader {
 
     Texel *new_texel_for_format(uint8_t gx_format) {
         switch (gx_format) {
+        case GX_CTF_R4: return new TexelI4;
         case GX_TF_I8: return new TexelI8;
         case GX_TF_IA8: return new TexelIA8;
         case GX_TF_RGBA8: return new TexelRGBA8;
@@ -390,6 +392,17 @@ struct PixelWriter {
             case GL_FLOAT:
                 return new DepthPixelStream<float>(format, type);
             }
+        } else if (format == GL_STENCIL_INDEX) {
+            switch (type) {
+            case GL_UNSIGNED_BYTE:
+                return new StencilPixelStream<uint8_t>(format, type);
+            case GL_UNSIGNED_SHORT:
+                return new StencilPixelStream<uint16_t>(format, type);
+            case GL_UNSIGNED_INT:
+                return new StencilPixelStream<uint32_t>(format, type);
+            case GL_FLOAT:
+                return new StencilPixelStream<float>(format, type);
+            }
         }
         switch (type) {
         case GL_UNSIGNED_BYTE:
@@ -435,17 +448,10 @@ void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height,
 {
     uint8_t gxformat = 0xff;
     const ReadPixelFormat *read_format = NULL;
+    ReadPixelFormat stencil_format;
     int n_components;
-
-    switch (format) {
-    case GL_COLOR_INDEX:
-        warning("glReadPixels: GL_COLOR_INDEX not supported");
-        return;
-    case GL_STENCIL_INDEX:
-        warning("glReadPixels: GL_STENCIL_INDEX not implemented");
-        // TODO
-        return;
-    }
+    void *texels = nullptr;
+    bool must_free_texels = false;
 
     for (int i = 0; s_read_pixel_formats[i].format != 0; i++) {
         if (s_read_pixel_formats[i].format == format) {
@@ -454,15 +460,27 @@ void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height,
         }
     }
     if (!read_format) {
-        warning("glReadPixels: unsupported format %04x", format);
-        return;
+        if (format == GL_STENCIL_INDEX) {
+            OgxEfbBuffer *stencil = _ogx_stencil_get_buffer();
+            stencil_format = {
+                format, 0,
+                uint8_t(GX_GetTexObjFmt(&stencil->texobj)), 1 };
+            read_format = &stencil_format;
+            texels = _ogx_efb_buffer_get_texels(stencil);
+        } else {
+            warning("glReadPixels: unsupported format %04x", format);
+            return;
+        }
     }
 
-    u32 size = GX_GetTexBufferSize(width, height,
-                                   read_format->gx_dest_format, 0, GX_FALSE);
-    void *texels = memalign(32, size);
-    _ogx_efb_save_area_to_buffer(read_format->gx_copy_format, x, y,
-                                 width, height, texels, OGX_EFB_NONE);
+    if (!texels) {
+        u32 size = GX_GetTexBufferSize(width, height,
+                                       read_format->gx_dest_format, 0, GX_FALSE);
+        texels = memalign(32, size);
+        _ogx_efb_save_area_to_buffer(read_format->gx_copy_format, x, y,
+                                     width, height, texels, OGX_EFB_NONE);
+        must_free_texels = true;
+    }
     TextureReader reader(read_format, texels, width, height);
     PixelWriter writer(data, width, height, format, type);
     for (int row = 0; row < height; row++) {
@@ -472,7 +490,10 @@ void glReadPixels(GLint x, GLint y, GLsizei width, GLsizei height,
             writer.write(&pixel);
         }
     }
-    free(texels);
+
+    if (must_free_texels) {
+        free(texels);
+    }
 }
 
 void glDrawPixels(GLsizei width, GLsizei height, GLenum format, GLenum type,

diff --git a/src/stencil.c b/src/stencil.c
@@ -630,6 +630,11 @@ void _ogx_stencil_clear()
     s_stencil_texture_needs_update = false;
 }
 
+OgxEfbBuffer *_ogx_stencil_get_buffer()
+{
+    return s_stencil_buffer;
+}
+
 void ogx_stencil_create(OgxStencilFlags flags)
 {
     s_wants_stencil = true;

diff --git a/src/stencil.h b/src/stencil.h
@@ -33,11 +33,16 @@ POSSIBILITY OF SUCH DAMAGE.
 #ifndef OPENGX_STENCIL_H
 #define OPENGX_STENCIL_H
 
+#include "efb.h"
 #include "opengx.h"
 
 #include <malloc.h>
 #include <stdbool.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 extern OgxStencilFlags _ogx_stencil_flags;
 
 void _ogx_stencil_enabled(void);
@@ -56,4 +61,10 @@ void _ogx_stencil_draw(OgxStencilDrawCallback callback, void *cb_data);
 void _ogx_stencil_load_into_efb();
 void _ogx_stencil_save_to_efb();
 
+OgxEfbBuffer *_ogx_stencil_get_buffer(void);
+
+#ifdef __cplusplus
+} // extern C
+#endif
+
 #endif /* OPENGX_STENCIL_H */