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| Alpha blending a triangle with a textured triangle in openGL |
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altalena
Member #13,639
October 2011
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in this program, I want to draw the triangles with the 3 corner colours interpolated smoothly blended with a repeating procedurally generated detail texture. I'm wondering if there's a way to draw a normal triangle, like this glBegin(GL_TRIANGLE_STRIP); glColor3d(0.75,0.25,0.25); glVertex3d( 0,1,0 ); glColor3d(0.25,0.75,0.25); glVertex3d( 1,0,0 ); glColor3d(0.25,0.25,0.75); glVertex3d( 1,1,0 ); glEnd(); with a repeating texture modifying the colour of each pixel in the triangle. The detail textures in Deus Ex are my inspiration for wanting to do this. Sorry if there's an obvious answer I should have found. ...At the briefest instant following creation all the matter of the universe was concentrated in a very small place, no larger than a grain of mustard. The matter at this time was very thin, so intangible, that it did not have real substance. It did have, however, a potential to gain substance and form and to become tangible matter. From the initial concentration of this intangible substance in its minute location, the substance expanded, expanding the universe as it did so. As the expansion progressed, a change in the substance occurred. This initially thin noncorporeal substance took on the tangible aspects of matter as we know it. From this initial act of creation, from this ethereally thin pseudosubstance, everything that has existed, or will ever exist, was, is, and will be formed. - the RaMBaN, 1194 - 1270 ג וּשְׁאַבְתֶּם-מַיִם, בְּשָׂשׂוֹן, מִמַּעַיְנֵי, הַיְשׁוּעָה. - Yeshayahu 12:3 |
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Trent Gamblin
Member #261
April 2000
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Assuming you're using Allegro and you have loaded the texture into a bitmap, then GLint tex = al_get_opengl_texture(allegro_bitmap); glEnable(GL_TEXTURE_2D); glBindTexture(GL_TEXTURE_2D, tex); glBegin(GL_TRIANGLES); glTexCoord3d(tu, tv) /* Define the rest of this vertex */ ... more vertices ... tu and tv are texture coordinates. In OpenGL by default those are from 0 (left and bottom) to 1 (right and top).
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altalena
Member #13,639
October 2011
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I tried what you suggested, but the program crashes now. Is there a short example program that just loads a .png and draws a textured triangle? edit: I attached the program I'm working on 1#include <GL/glu.h>
2ALLEGRO_BITMAP *image = NULL;
3image = al_load_bitmap("noise.png");
4GLuint texture = al_get_opengl_texture(image);
5if (texture != 0)
6 glBindTexture(GL_TEXTURE_2D, texture);
7glEnable(GL_DEPTH_TEST);
8glDepthMask(GL_TRUE);
9glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
10glMatrixMode(GL_PROJECTION);
11glLoadIdentity();
12gluPerspective(85,aspect_ratio,0.001,1000000);
13gluLookAt(eye[0],eye[1],eye[2], // camera is here
14 looking_at[0],looking_at[1],looking_at[2], // camera is looking towards this point
15 0.0f,0.0f,1.0f); // up vector
16
17glMatrixMode(GL_MODELVIEW);
18glLoadIdentity();
19glClear(GL_DEPTH_BUFFER_BIT);
20glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
21glClear(GL_DEPTH_BUFFER_BIT);
22
23glBegin(GL_TRIANGLES);
24glColor3d(0.5,0.5,0.5);
25glTexCoord2d(1, 1);
26glVertex3d( 1,1,0 );
27glTexCoord2d(1, 0);
28glVertex3d( 1,0,0 );
29glTexCoord2d(0, 1);
30glVertex3d( 0,1,0 );
31glEnd();
...At the briefest instant following creation all the matter of the universe was concentrated in a very small place, no larger than a grain of mustard. The matter at this time was very thin, so intangible, that it did not have real substance. It did have, however, a potential to gain substance and form and to become tangible matter. From the initial concentration of this intangible substance in its minute location, the substance expanded, expanding the universe as it did so. As the expansion progressed, a change in the substance occurred. This initially thin noncorporeal substance took on the tangible aspects of matter as we know it. From this initial act of creation, from this ethereally thin pseudosubstance, everything that has existed, or will ever exist, was, is, and will be formed. - the RaMBaN, 1194 - 1270 ג וּשְׁאַבְתֶּם-מַיִם, בְּשָׂשׂוֹן, מִמַּעַיְנֵי, הַיְשׁוּעָה. - Yeshayahu 12:3 |
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Trent Gamblin
Member #261
April 2000
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The code I posted will not crash as long as allegro_bitmap is valid.
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altalena
Member #13,639
October 2011
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Thanks. I'm gonna try http://wiki.allegro.cc/index.php?title=2D_using_OpenGL, and I'll edit if I get it to work. edit: I'm embarrassed to say I couldn't get it to work. Is there an example program anywhere that draws textured triangles? ...At the briefest instant following creation all the matter of the universe was concentrated in a very small place, no larger than a grain of mustard. The matter at this time was very thin, so intangible, that it did not have real substance. It did have, however, a potential to gain substance and form and to become tangible matter. From the initial concentration of this intangible substance in its minute location, the substance expanded, expanding the universe as it did so. As the expansion progressed, a change in the substance occurred. This initially thin noncorporeal substance took on the tangible aspects of matter as we know it. From this initial act of creation, from this ethereally thin pseudosubstance, everything that has existed, or will ever exist, was, is, and will be formed. - the RaMBaN, 1194 - 1270 ג וּשְׁאַבְתֶּם-מַיִם, בְּשָׂשׂוֹן, מִמַּעַיְנֵי, הַיְשׁוּעָה. - Yeshayahu 12:3 |
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