LAMW - DrawTexture Bug
lazarus / 43-Android

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Handoko · 2017-11-12 13:04

Tested on LAMW rev 684, jCanvasES2.DrawTexture always draws the
texture flipped horizontally. This issue also happens on AppDemo1 >
OpenGL2 2D, I compared the result on the screen and the original image
file, they're flipped.

I found the bug is in Laz_And-GLESv2_Canvas.pas:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Procedure
jCanvasES2.DrawTexture(const Texture : TxgElement; const Pt4 : Txy4CW;
Z : Single;                                 Alpha : Single; Effect :
TxgShader = Shader_Texture);var  T : Array[0..3] of TXY;  P :
Array[0..3] of TXYZ; // i : Integer;begin  //  if not FInitialized
then Exit;  P[0] := _XY_Z(Pt4[2],Z);  P[1] := _XY_Z(Pt4[1],Z);  P[2]
:= _XY_Z(Pt4[3],Z);  P[3] := _XY_Z(Pt4[0],Z);  //  T[0] := _XY(1,0); 
T[1] := _XY(1,1);  T[2] := _XY(0,0);  T[3] := _XY(0,1);  //  SetShader
 (Effect);  SetAlpha   (Alpha );  //  SetVertex  (@P );  SetColor  
(nil);  SetTexture (@T );  BindTexture(Texture);  // 
glDrawArrays(GL_TRIANGLE_STRIP,0,4);end;
Here is the code I suggest to fix the bug:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Procedure
jCanvasES2.DrawTexture(const Texture : TxgElement; const Pt4 : Txy4CW;
Z : Single;                                 Alpha : Single; Effect :
TxgShader = Shader_Texture);var  T : Array[0..3] of TXY;  P :
Array[0..3] of TXYZ;begin  //  if not FInitialized then Exit;  P[0] :=
_XY_Z(Pt4[2],Z);  P[1] := _XY_Z(Pt4[1],Z);  P[2] := _XY_Z(Pt4[3],Z); 
P[3] := _XY_Z(Pt4[0],Z);  //  T[0] := _XY(0,0);  T[1] := _XY(0,1); 
T[2] := _XY(1,0);  T[3] := _XY(1,1);  //  SetShader  (Effect); 
SetAlpha   (Alpha );  //  SetVertex  (@P );  SetColor   (nil); 
SetTexture (@T );  BindTexture(Texture);  // 
glDrawArrays(GL_TRIANGLE_STRIP,0,4);end;
The screenshots below are the test results using the original code
(left) and my suggestion (right):

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jmpessoa · 2017-11-12 17:44

Great!

I applied your patch!!

[and a minor change/fix in "androidwidgets.pas" to improve support to
jForm method "ReInit" 
and a "must have" fix in "androidthemes.pas" by @A.S to prevent IDE
crash when open multi-forms app like "AppDemo1"]

Thanks to All!