sokol: add screenshot function to OpenGL based backends (#12169)

thirdparty/sokol/sokol_gfx.h

@@ -4657,7 +4657,9 @@ _SOKOL_PRIVATE void _sg_dummy_update_image(_sg_image_t* img, const sg_image_data
 #if defined(_SOKOL_USE_WIN32_GL_LOADER)
 
 // X Macro list of GL function names and signatures
+// __v_ start
 #define _SG_GL_FUNCS \
+    _SG_XMACRO(glReadPixels,                      void, (GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, void * data)) \
     _SG_XMACRO(glBindVertexArray,                 void, (GLuint array)) \
     _SG_XMACRO(glFramebufferTextureLayer,         void, (GLenum target, GLenum attachment, GLuint texture, GLint level, GLint layer)) \
     _SG_XMACRO(glGenFramebuffers,                 void, (GLsizei n, GLuint * framebuffers)) \
@@ -4754,6 +4756,7 @@ _SOKOL_PRIVATE void _sg_dummy_update_image(_sg_image_t* img, const sg_image_data
     _SG_XMACRO(glGenVertexArrays,                 void, (GLsizei n, GLuint * arrays)) \
     _SG_XMACRO(glFrontFace,                       void, (GLenum mode)) \
     _SG_XMACRO(glCullFace,                        void, (GLenum mode))
+// __v_ end
 
 // generate GL function pointer typedefs
 #define _SG_XMACRO(name, ret, args) typedef ret (GL_APIENTRY* PFN_ ## name) args;

thirdparty/sokol/sokol_v.post.h

@@ -0,0 +1,9 @@
+#if defined(SOKOL_GLCORE33) || defined(SOKOL_GLES2) || defined(SOKOL_GLES3)
+	void v_sapp_gl_read_rgba_pixels(int x, int y, int width, int height, unsigned char* pixels) {
+		glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
+	}
+#else
+	void v_sapp_gl_read_rgba_pixels(int x, int y, int width, int height, unsigned char* pixels) {
+		// TODO
+	}
+#endif

thirdparty/sokol/sokol_v.pre.h

@@ -17,4 +17,3 @@
 	#define printf(...) __android_log_print(ANDROID_LOG_INFO, V_ANDROID_LOG_TAG_NAME, __VA_ARGS__)
 	#define fprintf(a, ...) __android_log_print(ANDROID_LOG_ERROR, V_ANDROID_LOG_TAG_NAME, __VA_ARGS__)
 #endif
-

vlib/sokol/c/declaration.c.v

@@ -49,10 +49,11 @@ $if gcboehm ? {
 	#define SOKOL_FREE GC_FREE
 }
 
-#include "sokol_v.h"
+#include "sokol_v.pre.h"
 #include "sokol_app.h"
 #define SOKOL_IMPL
 #define SOKOL_NO_DEPRECATED
 #include "sokol_gfx.h"
 #define SOKOL_GL_IMPL
 #include "util/sokol_gl.h"
+#include "sokol_v.post.h"

vlib/sokol/sapp/sapp_v.c.v

@@ -0,0 +1,50 @@
+module sapp
+
+import os
+
+// v_sapp_gl_read_rgba_pixels reads pixles from the OpenGL buffer into `pixels`.
+fn C.v_sapp_gl_read_rgba_pixels(x int, y int, width int, height int, pixels charptr)
+
+// screenshot takes a screenshot of the current window.
+[inline]
+pub fn screenshot(path string) ? {
+	if !path.ends_with('.ppm') {
+		return error(@MOD + '.' + @FN + ' currently only supports .ppm files.')
+	}
+
+	w := width()
+	h := height()
+
+	size := w * h * 4 //
+	mut pixels := []byte{len: size, init: 0}
+
+	C.v_sapp_gl_read_rgba_pixels(0, 0, w, h, pixels.data)
+
+	// TODO use separate thread for writing the data
+	// TODO use stbi to support more formats
+	// stbi.write_png(path, w, h, components, pixels.data, 3 * w)
+	// stbi.write_tga(path, w, h, components, pixels.data)
+	write_rgba_to_ppm(path, w, h, 4, pixels) ?
+
+	unsafe {
+		pixels.free()
+	}
+}
+
+// write_rgba_to_ppm writes `pixels` data in RGBA format to PPM3 format.
+fn write_rgba_to_ppm(path string, w int, h int, components int, pixels []byte) ? {
+	mut f_out := os.create(path) ?
+	f_out.writeln('P3') ?
+	f_out.writeln('$w $h') ?
+	f_out.writeln('255') ?
+	for i := h - 1; i >= 0; i-- {
+		for j := 0; j < w; j++ {
+			idx := i * w * components + j * components
+			r := int(pixels[idx])
+			g := int(pixels[idx + 1])
+			b := int(pixels[idx + 2])
+			f_out.write_string('$r $g $b ') ?
+		}
+	}
+	f_out.close()
+}