OpenGL2: Add OpenGL ES 2.0+ support

This mainly targets OpenGL ES 2.0 but it also supports compiling GLSL as
ESSL 3.00. It's missing support for framebuffer objects which should be
possible on ES 2. (Though using renderbuffers instead of textures.)

opengl1 cvars that are not supported will display a message and disable
the cvar. This has not been reviewed for new opengl2 cvars. Enabling
cvars may cause rendering issues. Some of the broken cvars may be
possible to support using OpenGL ES 3 features.

The game displays okay with the default cvars.

code/renderergl2/tr_init.c

@@ -451,21 +451,43 @@ Return value must be freed with ri.Hunk_FreeTempMemory()
 byte *RB_ReadPixels(int x, int y, int width, int height, size_t *offset, int *padlen)
 {
 	byte *buffer, *bufstart;
-	int padwidth, linelen;
-	GLint packAlign;
-	
+	int padwidth, linelen, bytesPerPixel;
+	int yin, xin, xout;
+	GLint packAlign, format;
+
+	// OpenGL ES is only required to support reading GL_RGBA
+	if (qglesMajorVersion >= 1) {
+		format = GL_RGBA;
+		bytesPerPixel = 4;
+	} else {
+		format = GL_RGB;
+		bytesPerPixel = 3;
+	}
+
 	qglGetIntegerv(GL_PACK_ALIGNMENT, &packAlign);
-	
-	linelen = width * 3;
+
+	linelen = width * bytesPerPixel;
 	padwidth = PAD(linelen, packAlign);
-	
+
 	// Allocate a few more bytes so that we can choose an alignment we like
 	buffer = ri.Hunk_AllocateTempMemory(padwidth * height + *offset + packAlign - 1);
-	
-	bufstart = PADP((intptr_t) buffer + *offset, packAlign);
 
-	qglReadPixels(x, y, width, height, GL_RGB, GL_UNSIGNED_BYTE, bufstart);
-	
+	bufstart = PADP((intptr_t) buffer + *offset, packAlign);
+	qglReadPixels(x, y, width, height, format, GL_UNSIGNED_BYTE, bufstart);
+
+	linelen = width * 3;
+
+	// Convert RGBA to RGB, in place, line by line
+	if (format == GL_RGBA) {
+		for (yin = 0; yin < height; yin++) {
+			for (xin = 0, xout = 0; xout < linelen; xin += 4, xout += 3) {
+				bufstart[yin*padwidth + xout + 0] = bufstart[yin*padwidth + xin + 0];
+				bufstart[yin*padwidth + xout + 1] = bufstart[yin*padwidth + xin + 1];
+				bufstart[yin*padwidth + xout + 2] = bufstart[yin*padwidth + xin + 2];
+			}
+		}
+	}
+
 	*offset = bufstart - buffer;
 	*padlen = padwidth - linelen;
 	
@@ -877,9 +899,10 @@ const void *RB_TakeVideoFrameCmd( const void *data )
 {
 	const videoFrameCommand_t	*cmd;
 	byte				*cBuf;
-	size_t				memcount, linelen;
+	size_t				memcount, bytesPerPixel, linelen, avilinelen;
 	int				padwidth, avipadwidth, padlen, avipadlen;
-	GLint packAlign;
+	int				yin, xin, xout;
+	GLint packAlign, format;
 
 	// finish any 2D drawing if needed
 	if(tess.numIndexes)
@@ -887,20 +910,32 @@ const void *RB_TakeVideoFrameCmd( const void *data )
 
 	cmd = (const videoFrameCommand_t *)data;
 	
+	// OpenGL ES is only required to support reading GL_RGBA
+	if (qglesMajorVersion >= 1) {
+		format = GL_RGBA;
+		bytesPerPixel = 4;
+	} else {
+		format = GL_RGB;
+		bytesPerPixel = 3;
+	}
+
 	qglGetIntegerv(GL_PACK_ALIGNMENT, &packAlign);
 
-	linelen = cmd->width * 3;
+	linelen = cmd->width * bytesPerPixel;
 
 	// Alignment stuff for glReadPixels
 	padwidth = PAD(linelen, packAlign);
 	padlen = padwidth - linelen;
+
+	avilinelen = cmd->width * 3;
+
 	// AVI line padding
-	avipadwidth = PAD(linelen, AVI_LINE_PADDING);
-	avipadlen = avipadwidth - linelen;
+	avipadwidth = PAD(avilinelen, AVI_LINE_PADDING);
+	avipadlen = avipadwidth - avilinelen;
 
 	cBuf = PADP(cmd->captureBuffer, packAlign);
 		
-	qglReadPixels(0, 0, cmd->width, cmd->height, GL_RGB,
+	qglReadPixels(0, 0, cmd->width, cmd->height, format,
 		GL_UNSIGNED_BYTE, cBuf);
 
 	memcount = padwidth * cmd->height;
@@ -911,7 +946,21 @@ const void *RB_TakeVideoFrameCmd( const void *data )
 
 	if(cmd->motionJpeg)
 	{
-		memcount = RE_SaveJPGToBuffer(cmd->encodeBuffer, linelen * cmd->height,
+		// Convert RGBA to RGB, in place, line by line
+		if (format == GL_RGBA) {
+			linelen = cmd->width * 3;
+			padlen = padwidth - linelen;
+
+			for (yin = 0; yin < cmd->height; yin++) {
+				for (xin = 0, xout = 0; xout < linelen; xin += 4, xout += 3) {
+					cBuf[yin*padwidth + xout + 0] = cBuf[yin*padwidth + xin + 0];
+					cBuf[yin*padwidth + xout + 1] = cBuf[yin*padwidth + xin + 1];
+					cBuf[yin*padwidth + xout + 2] = cBuf[yin*padwidth + xin + 2];
+				}
+			}
+		}
+
+		memcount = RE_SaveJPGToBuffer(cmd->encodeBuffer, avilinelen * cmd->height,
 			r_aviMotionJpegQuality->integer,
 			cmd->width, cmd->height, cBuf, padlen);
 		ri.CL_WriteAVIVideoFrame(cmd->encodeBuffer, memcount);
@@ -934,7 +983,7 @@ const void *RB_TakeVideoFrameCmd( const void *data )
 				*destptr++ = srcptr[2];
 				*destptr++ = srcptr[1];
 				*destptr++ = srcptr[0];
-				srcptr += 3;
+				srcptr += bytesPerPixel;
 			}
 			
 			Com_Memset(destptr, '\0', avipadlen);