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Save and restore GL parameters as appropriate

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According to the docs "glPixelStorei sets pixel storage modes that
affect the operation of subsequent glReadPixels as well as the
unpacking of texture patterns (see glTexImage2D and glTexSubImage2D)."

Hence we
(a) must be aware that current values of these modes can be anything
    set by user or FLTK code before
(b) should be polite and restore these modes to previous values

See discussion in fltk.coredev, thread "gl_draw problem" started on
Apr 05, 2019.
This commit is contained in:
Albrecht Schlosser
2019-04-10 17:02:04 +02:00
parent cb7dbc34d7
commit 3bbc453237
1 changed files with 16 additions and 4 deletions
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src/gl_draw.cxx
+16 -4
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@@ -217,9 +217,12 @@ void gl_rect(int x, int y, int w, int h) {
void gl_draw_image(const uchar* b, int x, int y, int w, int h, int d, int ld) {
if (!ld) ld = w*d;
GLint row_length;
glGetIntegerv(GL_UNPACK_ROW_LENGTH, &row_length); // get current row length
glPixelStorei(GL_UNPACK_ROW_LENGTH, ld/d);
glRasterPos2i(x,y);
glDrawPixels(w,h,d<4?GL_RGB:GL_RGBA,GL_UNSIGNED_BYTE,(const ulong*)b);
glPixelStorei(GL_UNPACK_ROW_LENGTH, row_length); // restore row length
}
@@ -404,18 +407,24 @@ int gl_texture_fifo::compute_texture(const char* str, int n)
int w, h;
w = fl_width(fifo[current].utf8, n) * gl_scale;
// Hack - make w be aligned
w = (w + 3) & 0xFFFFFFC;
w = (w + 3) & (~3);
h = fl_height() * gl_scale;
fifo[current].scale = gl_scale;
fifo[current].fdesc = gl_fontsize;
char *txt_buf = Fl_Gl_Window_Driver::global()->alpha_mask_for_string(str, n, w, h);
// save GL parameters GL_UNPACK_ROW_LENGTH and GL_UNPACK_ALIGNMENT
GLint row_length, alignment;
glGetIntegerv(GL_UNPACK_ROW_LENGTH, &row_length);
glGetIntegerv(GL_UNPACK_ALIGNMENT, &alignment);
// put the bitmap in an alpha-component-only texture
glPushAttrib(GL_TEXTURE_BIT);
glBindTexture (GL_TEXTURE_RECTANGLE_ARB, fifo[current].texName);
glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
//glPixelStorei(GL_UNPACK_ROW_LENGTH, w);
glPixelStorei(GL_UNPACK_ROW_LENGTH, w);
glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
// GL_ALPHA8 is defined in GL/gl.h of X11 and of MinGW32 and of MinGW64 and of OpenGL.framework for MacOS
glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, GL_ALPHA8, w, h, 0, GL_ALPHA, GL_UNSIGNED_BYTE, txt_buf);
/* For the record: texture construction if an alpha-only-texture is not possible
@@ -424,6 +433,9 @@ int gl_texture_fifo::compute_texture(const char* str, int n)
*/
delete[] txt_buf; // free the buffer now we have copied it into the Gl texture
glPopAttrib();
// restore saved GL parameters
glPixelStorei(GL_UNPACK_ROW_LENGTH, row_length);
glPixelStorei(GL_UNPACK_ALIGNMENT, alignment);
return current;
}